Contraceptive Steroid Effects on Lipids and Lipoproteins in Cynomolgus Monkeys. John S. Parks, Susan J. Pelkey, John Babiak, and Thomas B.

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1 Contrceptive Steroid Effects on Lipids nd Lipoproteins in Cynomolgus Monkeys John S. Prks, Susn J. Pelkey, John Bbik, nd Thoms B. Clrkson Seventy-three dult femle cynomolgus monkeys fed n therogenic diet were studied to determine the effect of two different combintion contrceptive steroid preprtions contining equivlent mounts of estrogen but different progestln components on plsm NpkJs nd lipoproteins. ur hypothesis ws tht ny high density llpoproteln (HDL) lowering effect of the contrceptive steroid preprtions ws proportionl to the rise In totl serum cholesterol cused by the progestins. For 2 yers, one group (vrl [Wyeth Lbortories], n=23) received 75 HQ norgestrel nd 7.5 ng ethinyl estrdiol dlly, while nother (Demulen [Serle & Co.], n=25) received 150 /tg ethynodlol dlcetto nd 7.5 /ig ethinyl estrdiol dlly. The control group (n=24) received no tretment n verge, the two orl contrceptive groups hd higher totl serum cholesterol nd triglycerlde concentrtions but lower HDL cholesterol concentrtions nd smller low density lipoproteins (LDL) compred with the control group. There ws n Inverse reltionship between totl serum cholesterol nd HDL cholesterol for ll three groups, but t ny given totl serum cholesterol concentrtion between 350 nd 500 mg/dl, the vrl group hd HDL cholesterol concentrtions tht verged 37% nd 14% lower thn the control nd Demulen groups, respectively. The decrese In HDL concentrtions with orl contrceptive tretment ws ssocited with shrp decrese In (HDL,),^, protein (82% for vrl nd 59% for Demulen) nd corresponding Increse In (HDLi*^)^. protein s determined by grdient gel electrophoresls. f 23 nimls In the vrl group, six hd HDL subtrctions >10 nm dimeter (HDLJgg. compred with 22 of 24 nimls in the control group. Although LDL size, on verge, ws smller nd plsm triglycerides were greter with orl contrceptive tretment compred with controls, there ws no pprent reltionship between LDL size nd plsm trlglyceride concentrtions. We conclude tht: 1) the smller LDL prticles of Demulen vs. control femle cynomolgus monkeys ws not relted to the differences In plsm triglycerlde concentrtions between the two groups, nd 2) tretment of femle cynomolgus monkeys fed cholesterol with vrl results in dditionl HDL» lowering compred with tht of dietry cholesterol lone or dietry cholesterol with Demulen. (Arteriosclerosis 9: , Mrch/April 1989) rl contrceptives usully contin synthetic estrogen (i.e., ethinyl estrdiol) nd one of severl synthetic progestins. Since estrogen nd progestins ech ffect lipoprotein metbolism in unique wys, combined therpy cn result in vriety of plsm lipoprotein chnges tht depend on the reltive mounts nd kinds of the two steroids. Most estrogens increse plsm high density lipoprotein (HDL) concentrtions, while most combintion orl contrceptives cuse decrese in plsm HDL due to the progestin component. 1-2 Mny orl contrceptives increse plsm low density lipoprotein (LDL) From the Deprtment of Comprtive Medicine, Bowmn Gry School of Medicine, Wke Forest University Medicl Center, 300 South Hwthorne Rod, Winston-Slem, North Crolin. This reserch ws supported by Ntionl Hert, Lung, nd Blood Institute Grnt #HL14164 (Specilized Center of Reserch in Arteriosclerosis) nd Contrct HD from the Ntionl Institute of Child Helth nd Humn Development. John Bbik is t the Deprtment of PredinicJ Reserch, Sndoz Reserch Institute, Est Hnover, New Jersey. Address for reprints: John S. Prks, Deprtment of Comprtive Medicine, Bowmn Gry School of Medicine, 300 South Hwthorne Rod, Winston-Slem, NC Received June 1,1988; revision ccepted November 23,1988. concentrtions. 3 In prticulr, n increse in the concentrtion of smll, dense LDL prticles hs been reported, wheres lrger, less dense LDL prticles my ctully decrese in concentrtion. 4 There hs been concern bout these effects of orl contrceptives on lipoprotein metbolism becuse the chnges re in the direction of possible incresed risk of coronry hert disese. For il our studies on contrceptive steroids, we hve chosen to study femle cynomolgus monkeys (Mcc fsciculris) becuse, like women, these nimls respond to orl contrceptive tretment with mrked increses in plsm triglyceride (TG) concentrtions nd decreses in plsm HDL concentrtions, prticulrly the HDL 2 subtrction. 567 Since n inverse reltionship between totl serum cholesterol (TSC) nd HDL cholesterol (HDL-C) exists for hypercholesterolemic monkeys (TSC>200 mg/ dl), 8 we were interested in exploring the interreltionship between TSC nd HDL-C in monkeys given progestins of differing structures nd phrmcologicl effects with n equivlent mount of estrogen. We hypothesized tht ny HDL-lowering effect of the contrceptive steroid preprtions would be, s seen with dietry hypercholesterolemi, proportionl to the rise in TSC cused by the 261

2 262 ARTERISCLERSIS VL 9, No 2, MARCH/APRIL 1989 Tble 1. Effects of rl Contrceptive Tretment on Plsm Uplds nd Upoprotelns of Femle Cynomolgus Monkeys Group Pretretment Control (n=24) vrl (n=23) Demulen (n=26) p vlue* Control vs. vrl TSC (mg/dl) 316±26 295±27 329±26 HDL-C (mg/dl) Control vs. Demulen vrl vs. Demulen Posttretment Control (n=24) vrl (n=23) Demulen (n=26) p vlue* Control vs. vrl Control vs. Demulen vrl vs. Demulen Pre- vs. posttretmentt Control (n=24) vrl (n=23) Demulen (n=26) 270± ±28 362± ±7 33±3 41 ± ±3 40±5 57± ± ± 3.14± Vlues were determined on single blood smple from ech niml tken 2 months before orl contrceptive tretment (pretretment) nd between 21 nd 23 months fter tretment (posttretment). Vlues re mens±sem. 'Anlysis of vrince with Fisher's lest significnt difference test; =not significnt t p=. tpired f test ±6 72±8 TG (mg/dl) 25±3 23±3 18±2 LDL-MW (g//imol) 3.43± ± ±0.08 progestins. In the experiment reported here, the effects of norgestrel/ethinyl estrdiol contining orl contrceptive on plsm lipoproteins of femle monkeys were compred with those of preprtion contining ethynodiol dicette/ethinyl estrdiol. These femle monkeys were fed modertely therogenic diet for 31 months during which orl contrceptive tretment ws given for 2 yers. Methods Animls Seventy-three dult femle cynomolgus mcques (Mcc fsciculris) were used for the study. The nimls were fed for 31 months modertely therogenic diet, supplied by Bioserve Inc. (Frenchtown, NJ), tht contined 0.39 mg cholesterol/kcl nd 38% of clories s sturted ft (lrd). Experimentl Design The study ws divided into two periods: 7-month bseline nd 24-month experimentl period. During the bseline period, the nimls consumed the therogenic diet, nd blood smples were tken for TSC nd HDL-C determintions. Using strtified rndomiztion technique, the nimls were ssigned to either the control group or to one of two tretment groups bsed on body weight, TSC, HDL-C, nd menstrul cycle history. After ssignment of ll nimls into one of the three groups, the men nd vrince of TSC, HDL-C, body weight, nd number of menstrul cycles of ech of the three groups were essentilly the sme (Tble 1). During the 24-month experimentl period, one group received 75 fig norgestrel nd 7.5 fig ethinyl estrdiol dily (vrl, Wyeth Lbortories, Phildelphi, PA), nd nother group received 150 fig ethynodiol dlcette nd 7.5 fig ethinyl estrdiol dily (Demulen, Serie & Co., Sn Jun, Puerto Rico). The contrceptive steroid pills were ground with mortr nd pestle nd incorported into the ground diet with mixer. The lbortory prepred diets were kept frozen until time for feeding. rl contrceptive dosges for these nimls were equivlent, on cloric intke bsis, to humn femles consuming 1800 kcl nd 1 orl contrceptive pill per dy. The control group received no contrceptive steroids. Llpld nd Llpoproteln Quntlttlon At 2-month intervls throughout the bseline nd experimentl periods, blood smples were tken from ll nimls to quntitte TSC, HDL-C, nd serum TG concentrtions. TSC nd TG concentrtions were determined by n utonlyzer method using LJpid Reserch Clinic methodology. 9 HDL-C concentrtions were quntitted fter precipittion of poprotein (po) B contining lipoprotein from serum with heprin-mngnese. 10 Low Density Llpoproteln Moleculr Weight Determintion LDL moleculr weight mesurements were mde for ll nimls during the bseline period (5 months fter diet

3 EFFECTS F RAL CNTRACEPTIVES N LIPPRTEI Prks et l. 263 initition; 2 months before tretment strted) nd fter 24 months of orl contrceptive tretment. Blood smples were obtined from the femorl vein of fsted nimls fter intrmusculr dministrtion of ketmine (10 mg/kg). Blood ws collected in tubes contining 0.1% EDTA, 0.02% NN 3, 0.04% DTNB, ph 7.4 (finl concentrtion), nd this ws immeditely plced on ice. Plsm ws hrvested by low speed centrifugtion t 4 C. The lipoproteins were isolted from plsm by uttrcentrifugtion nd grose column chromtogrphy. 11 With this procedure, LDL size (i.e., LDL moleculr weight) ws determined for ech smple by including trce mount of n iodinted LDL preprtion of known moleculr weight. 11 Grdient Gel Electrophoresls Prepoured polycrylmide grdient gels (4% to 30%; Phrmci, Pisctwy, NJ) were used to investigte HDL subfrction size heterogeneity. Gels were run s described previously. 12 Briefly, d<1.225 g/ml lipoproteins (four prts) were mixed with one prt of solution consisting of 40% sucrose nd 0.01% bromphenol blue, nd 10 to 20 /xl liquot contining 10 fig protein ws pplied to the gels. Gels were subjected to electrophoresis for 24 hours t 125 volts (10 C). After electrophoresls, gels were stined with Coomssie blue G-250 nd were destined in 5% cetic cid. After destlning, the gels were scnned using lser densitometer, nd the percentge HDL subfrction protein distribution ws clculted from the re units. Clcultion of HDL prticle size ws bsed on the mobility of protein stndrds of known Stokes' dimeters. Sttistics All vlues re reported s mens±stndrd error. Sttisticl comprisons were mde between control nd tretment groups by using nlysis of vrince nd Fisher's lest significnt difference test. A pired f test ws used for comprisons before nd fter tretment within single group. Results Tble 1 contins the TSC, HDL-C, nd TG concentrtions nd the LDL moleculr weight vlues for the three groups of nimls during the bseline period (5 months fter diet initition) nd fter 21 to 23 months of tretment. There ws no significnt difference in ny lipid or lipoprotein mesurements mong groups during the bseline period. As expected, the lipid nd lipoprotein mesurements for the control group were similr fter the 24-month experimentl period compred with the pre-experimentl (bseline) vlues. The vrl tretment group hd significnt increse in plsm TG (p<0.01) nd significnt decrese in HDL-C (p=0.01) fter tretment compred with bseline vlues. LDL moleculr weight nd TSC fter vrl tretment were not significntly different compred with pretretment vlues. After 21 to 23 months of tretment, the vrl group hd 50% less HDL-C compred with the controls. TSC, TG, nd LDL moleculr weight were not significntly different between the vrl nd control group fter the tretment period. The Demulen group responded in mnner tht ws qulittively similr to tht of the vrl group. After 21 to 23 months of Demulen tretment, TG were significntly incresed, nd HDL-C nd LDL moleculr weight were significntly decresed compred with the preexperimentl vlues (Tble 1). Compred with the control group t 21 to 23 months of tretment, the Demulen group hd significntly higher TSC nd TG concentrtions nd significntly lower HDL-C concentrtions nd smller LDL. After 21 to 23 months of tretment, the only significnt difference between the vrl versus Demulen groups ws high TG concentrtions for the Demulen group. Next, the interreltionship between TSC, TG, nd HDL- C concentrtions for the three groups of nimls were exmined. To do this, the verge bimonthly TSC or TG vlues for ech group tken throughout the bseline nd experimentl periods were plotted with the corresponding HDL-C vlue s shown in Figure 1. Note tht ech point in Figure 1 represents the men of 23 to 26 nimls in its respective group. There ws n inverse reltionship between TSC nd HDL-C concentrtions: s TSC incresed, HDL-C decresed. Interestingly, the control nd Demulen vlues ppered to fll on the sme regression line, while the vrl vlues were uniformly lower. At ny given TSC concentrtion from 375 to 500 mg/dl, the vrl group hd significntly (p<0.01) lower HDL-C concentrtions compred with the control nd Demulen groups (32±1, 50±1, nd 43±1 mg/dl HDL-C, respectively). A similr reltionship ws found when plsm TG concentrtions were plotted with HDL-C, tht is, n inverse reltionship ws found between TG nd HDL-C. The vrl group hd lower HDL-C concentrtions t ny given TG concentrtion compred with the control nd Demulen groups. To exmine the effect of orl contrceptive tretment on HDL subfrction size distribution, grdient gel electrophoresls ws used to further subfrctionte HDL. The frequency of occurrence of different HDL size popultions for the three groups ws exmined first. These dt re shown in Figure 2. The R, vlues previously determined for HDL subclsses of humn HDL re indicted by the verticl lines. The most striking difference in HDL subfrction distribution with orl contrceptive tretment ws found for the vrl group. nly 6 of 23 nimls in the vrl group hd HDL subtrctions >100 A In dimeter (HDL,)^, compred with 22 of 24 nimls in the control group. The Demulen group ws intermedite between the control nd vrl groups with 15 of 24 nimls hving detectble (HDL^gg. subtrctions. A similr, but less striking trend ws seen for the (HDL^Jgg, subfrction. Using the nomenclture of Blnche et l. 12 nd the subfrction size rnges estblished for humn popultion, we quntitted the percentge protein distribution of HDL subtrctions for the three groups of nimls by using lser densitometry. The demrctions of ech subfrction size rnge re shown in Figure 2. Tble 2 summrizes the dt from these nlyses. HDL protein ws pproximtely eqully distributed mong ll four HDL subclsses for the control nimls. Both contrceptive steroid tretments

4 264 ARTERISCLERSIS VL 9, No 2, MARCH/APRIL 1989 Q DC o TTAL SERUM CHLESTERL (MG/DL) ^ 80- _J Q -i 60 o DC r- V> -i 40- X on - A m A A _ D " n " EL A CNTRL * VRAL DEMULEN "» " " A m * * * A A A A * SERUM TRIGLYCERIDES (MG/DL) B Figure 1. Reltionships between totl serum cholesterol (A), serum triglyceride (B), nd HDL cholesterol (A nd B) concentrtions (mg/dl) for femle cynomolgus monkeys treted with orl contrceptives. Points represent the verge bimonthly vlues for the groups tken throughout the bseline nd experimentl periods; ech point is the men of 23 to 26 individul nimls. Points representing the vrl nd Demulen groups in the upper left qudrnt of ech pnel were tken during the bseline period. At totl serum cholesterol concentrtions >375 mg/dl, the verge high density lipoprotein cholesterol (HDL-C) concentrtions were 50±1,32+1, nd 43±1 for the control, vrl, nd Demulen groups, respectively. were ssocited with sttisticlly significnt decrese in the percentge of (HDL)^, protein (lrgest subtrctions) nd corresponding increse in (HL^ggt protein (smllest subtrctions). However, the difference in (HDL,),,, distribution ws not sttisticlly significnt between the two orl contrceptive tretment groups. HDL subtrctions of intermedite size [(HDLjJgg, nd (HDU^gJ were similr for control, vrl, nd Demulen groups. To exmine the effect of totl HDL concentrtions on the HDL subtrction distribution mong the three groups, we plotted HDL-C ( mesure reflective of totl HDL) versus the percentge HDL subtrction protein distribution. The results re shown in Figure 3. There ws n increse in the percentge of (HDL,),,,, protein with incresing HDL-C concentrtions. Note tht mny of the vrl-treted nimls hd vlues long the bsciss, indicting tht they hd no detectble (HDL),^,. The percentge (HDL,^),^ protein showed mrked decrese s HDL-C incresed. rl contrceptive tretment ws ssocited with n increse in plsm TG nd decrese in LDL size (Tble 1). Since we hd previously found n inverse reltionship between LDL size nd plsm TG concentrtions, 13 plot of the individul vlues of these vribles for the three groups of nimls ws mde (Figure 4). There ws no pprent reltionship between LDL size nd plsm TG concentrtions over the rnge of vlues found in this study. Discussion This study ws undertken to determine the effect of two orl contrceptive formultions with the sme dose nd kind of estrogen but with different progestins on the plsm lipid nd lipoprotein concentrtions nd HDL subtrction distribution of femle cynomolgus monkeys. This niml model ws chosen becuse we hd previously shown tht this species is suitble for studies on the effect of contrceptive steroids on plsm lipoproteins nd therosclerosis. 587 Both contrceptive formultions contined equivlent mounts of ethinyt estrdiol (7.5 HQ dily) but different progestins; the Demulen group received 150 ng of ethynodiol dicette dily while the vrl group received 75 fug of norgestrel dily. The two orl contrceptive groups, on verge, hd higher TSC nd TG concentrtions but lower HDL cholesterol concentrtions nd smller LDL compred with the control group. The (HDL),,. subtrction protein ws mrkedly reduced nd the (HDL^),,,, ws incresed for the orl contrceptive groups. Similr findings in women tking combintion orl contrceptives nd in cynomolgus monkeys given vrl 19 hve been reported. In the ltter study, vrl tretment resulted in significnt reduction of HDLj concentrtions (mesured by nlyticl ultrcentrifugtjon) nd LDL size compred with the femle control group; totl plsm cholesterol concentrtions were not significntly different between the two groups. 19 The present study extends our initil findings to investigte the interreltionships between plsm lipids nd lipoproteins when two orl contrceptive formultions contining different progestins re used nd to test our hypothesis tht the HDL lowering effect of the two orl contrceptive preprtions ws proportionl to the increse in TSC cused by the progestins. Despite the HDL lowering induced by both orl contrceptives, coronry rtery therosclerosis ws not excerbted nd ws reduced mong

5 EFFECTS F RAL CNTRACEPTIVES N LIPPRTEI Prks et l. 265 Prticle Dimeter, nm b b,c All Groups ! 4-8- Control n 6- vrl Rf Reltive to Albumin Figure 2. Histogrm of high density lipoprotein (HDL) subfrction size for femle cynomolgus monkeys treted with orl contrceptives. d<1.225 g/ml lipoproteins from ech niml were seprted on 4% to 30% polycrylmide grdient gels, nd stined gels were scnned with lser densitometer. Pek Rf vlues for ech HDL subfrction reltive to lbumin were plotted for ech niml. The prticle dimeter scle ws generted by using moleculr weight stndrds of known Stokes' dimeters.12 Verticl dshed lines indicte the HDL subfrction size rnges reported for humn popultion.12 the monkeys t highest risk on the bsis of their lipid profile (unpublished dt). Perhps the most striking effect of orl contrceptive tretment ws its effect on HDL concentrtions nd subfrction distribution. In generl, when nonhumn primtes become hypercholesterolemic by consuming dietry cholesterol nd sturted ft, there is decrese in HDL concentrtions nd redistribution of HDL subfrction mss; lrger, less dense HDL2b subtrctions decrese in n mount reltive to the smller, more dense HDL3 subtrctions.8 The sme trend ppers to occur for the control nd Demulen groups; s TSC incresed there ws proportionl decrese in HDL-C (Figure 1 A). In ddition, s HDL-C decresed, the proportion of (HDL2b)gge

6 266 ARTERISCLERSIS VL 9, No 2, MARCH/APRIL 1989 Tble 2. HDL Subtrction Protein Distribution Determined by Grdient Gel Electrophoresls o. z Q. Group HDL HDLj. HDL3. Control (n=24) vrl (n=23) ±2.5* 23.2± ± ± ± ± ±5.4* Demulen (n=25) * 19.6± ± ±3.6* Vlues re mens±sem. "Significntly different from the control group (p<) by nlysts of vrince nd Fisher's lest significnt difference test. (HDL 2b)gge D uu " 75" 50; 25 : i i i 1 CNTRL VRAL DEMULEN 1 c D ' D e r HDL CHLESTERL (MG/DL) A (HDL 3b,c)gge * *» D D tp D o B HDL CHLESTERL (MG/DL) Figure 3. Plot of high density lipoprotein (HDL) cholesterol concentrtions (mg/dl) vs. percentge of HDL (A) nd HDL,^ (B) protein for femle cynomo<gus monkeys treted with orl contrceptives for 2 yers. Percentge HDL protein distribution ws determined by grdient gel electrophoresis. 12 Ech point represents dt from n individul niml. decresed nd (HLs^gg, incresed (Figure 3). However, these reltionships were not observed for the vrltreted group. HDL-C concentrtions were uniformly lower thn the control or Demulen groups regrdless of TSC concentrtions (Figure 1, Top) nd there were few HDL d _J i 4.5" 3.5- D + ' f CNTRL + VRAL DEMULEN SERUM TRIGLYCERIDES (MG/DL) Figure 4. Plot of serum triglycerides (mg/dl) vs. low density lipoprotein (LDL) moleculr weight (MW) for femle cynomolgus monkeys treted wtth orl contrceptives for 2 yers. LDL moleculr weight (gvmol) ws mesured by grose column chromtogrphy. 11 Ech point represents the vlue for n individul niml. prticles in the (HDLJgge size rnge for the vrl group (Figure 2). Thus, even though Demulen tretment resulted in higher verge degree of hypercnolesterolemi thn vrl tretment, the HDL cholesterol concentrtions were 26% lower for the ltter group when TSC concentrtions were greter thn 375 mg/dl (Figure 1). These results suggest: 1) tht for n equivlent degree of hypercholesterolemi, vrl tretment results in dditionl HDL lowering compred with tht of dietry cholesterol lone or dietry cholesterol with different progestin (i.e., ethynodiol dicette), nd 2) tht this lowering occurs in the HDL, size rnge (Tble 2). The decrese in HDL concentrtions wtth vrl tretment my be secondry to n incresed ctbolism of po A-1 s suggested for nbolic steroid therpy 20 or my result from decresed production of HDL precursor prticles by the liver. Progestjns lone given to women hve reportedly decresed plsm concentrtions of TG nd HDL 2 nd incresed heptic lipse ctivity, while estrogenic gents hve the opposite effect. When combintion contrceptive steroids re given, the plsm lipoprotein response depends on the dosge nd biologicl effects of the progestin nd the dosge of the estrogen component. 1 Severl studies hve exmined the effect of vrl nd Demulen on lipo-

7 EFFECTS F RAL CNTRACEPTIVES N LIPPRTEI Prks et l. 267 protein concentrtions of women. vrl tretment ws ssocited with n increse in plsm TG, n increse or no chnge 14 in totl plsm nd LDL cholesterol, nd decrese in HDL-C Demulen tretment ws ssocited with n increse in plsm TG, n increse or no chnge 14 in totl plsm cholesterol, n increse 17 or no chnge in LDL cholesterol, nd no chnge in HDL-C concentrtions. 314 Mny of the sme responses were seen in the vrl nd Demulen treted nimls of this study. It hs been suggested tht the decrese in HDL 2 concentrtions ccompnying progestin dministrtion is relted to n increse in heptic lipse ctivity. 1 However, in studies of subset of our nimls, heptic TG lipse ws reduced 20% to 35% with orl contrceptive tretment compred with controls, but lipoprotein lipse ctivity ws similr for ll three groups. 21 Thus, the ethinyl estrdiol component of these two contrceptive formultions ppered to hve predominnt effect on plsm TG concentrtions nd heptic lipse ctivity. However, HDL concentrtions nd subtrction distribution pper to be influenced more by the progestin by mechnisms tht presumbly include synthesis nd ctbolism of HDL or other intrvsculr metbolic events tht modify HDL (i.e., lecithin:cholesterol cyttrnsferse) nd not by heptic lipse ctivity. LDL size mesured s LDL moleculr weight ws significntly smller for the Demulen-treted group compred with control nimls. LDL moleculr weight is strong positive predictor of the extent nd severity of coronry rtery therosclerosis in nonhumn primtes. 22 Diet-induced hypercholesterolemi in mle cynomolgus monkeys is ssocited with n increse in LDL size, but for femle cynomolgus monkeys it is ssocited with n increse in the number, not size, of LDL prticles in plsm. 23 However, fctors tht control LDL prticle size re poorly understood. ne hypotheticl mechnism involves TG for cholesteryl ester (CE) exchnge. In this scheme, s plsm TG concentrtions increse, there is TG for LDL CE exchnge. Subsequent hydrolysis of the exchnged TG results in reduction of LDL size. If this proposed mechnism were responsible for the smller LDL of the Demulen group, which hd higher TG concentrtions, then n inverse reltionship between LDL size nd plsm TG concentrtions would be expected. However, such reltionship ws not pprent over the rnge of plsm TG vlues in this study (Figure 4). This is in contrst to hypertriglyceridemic humns 13 nd to ethnolinduced hypertriglyceridemic monkeys (reference 24 nd LL Rudel, personl communiction), both of which demonstrted n inverse reltionship between LDL size nd plsm TG concentrtions. Therefore, orl contrceptive tretment pprently ffects LDL size by different mechnisms. In t lest one other species of nonhumn primtes, the Africn green monkey, strong correltion between LDL size nd heptic CE content, s well s heptic very low density lipoprotein cholesterol secretion, hs been found (JS Prks, FL Johnson, nd LL Rudel, unpublished observtions). Whether such reltionship exists in the nimls of this study is unknown. Acknowledgments The uthors thnk Lind dhm for her ssistnce with the mnuscript preprtion. References 1. Tlkknen MJ, Nlkkil EA. rl contrceptives nd lipoprotein metbolism. J Reprod Med 1986;31: Brdley DD, Wlngerd J, Pettttl DB, Kruu RM, Rmchrn S. Serum high density lipoprotein cholesterol in women using orl contrceptives, estrogen nd progestins. N Engl J Med : Whl P, Wkfen C, Knopp R, et l. Effect of estrogenprogestin potency on Hpld/lipoproteJn cholesterol. N Engl J Med 1983:308: Kruu RM. Contrceptive steroid effects on serum lipoprotelns nd lipoprotein subclsses. In: Btye R, Gregoire A, eds. Contrceptive steroids: Phrmcology nd sfety. New York: Plenum, 1986: Korttnlk DR, Clrkon TB, Adms MR. Cynomolgus mcques s models for evluting effects of contrceptive steroids on plsm lipoprotein nd coronry rtery therosclerosis. In: Blye R, Gregoire A, eds. 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8 268 ARTERISCLERSIS VL 9, No 2, MARCH/APRIL Adms MR, Clrfcson TB, Rudel LL, Korttnlk DR, Nsh HA. Effect of contrceptive steroids on the plsm lipoproteins nd coronry rtery therosclerosis of femle cynomolgus mcques. In: Eker ED, Pckrd ED, Wenger NK, Clrkson TB, Tyroler HA, eds. Coronry hert disese in women. Proceedings of n N.I.H. Workshop. New York: Hymrket Doym, Inc. 1987: Hffner SM, Kushwh S, Foster DM, Applebum- Bowden D, Hzzrd WR. Studies on the metbolic mechnisms of reduced high density lipoproteins during nbolic steroid therpy. Metbolism 1983;32: Str RJ. LJpoprotein lipse nd heptic triglycerlde lipse studies in nonhumn primtes: reltionship to high density lipoprotein subclsses nd serum lipids. [MS thesis], Wke Forest University, Rudel LL, Prks JS, Johnson FL, Bblk J. Low density lipoproteins in therosclerosis. J Upid Res 1986;27: Rudel LL, Pitts LL Mle-femle vribility in the dietry cholesterol-induced hyperiipoprotelneml of cynomolgus monkeys (Mcc fsdculris). J Upid Res 1978;19: Rudel LL, Lethers CW, Bond MG, Bullock BC. Dietry ethnol-induced modifictions in hyperiipoproteinemi nd therosclerosis in nonhumn primtes (Mcc nemestrin). Arteriosclerosis 1981 ;1: Index Terms: contrceptive steroids vrl Demulen HDL subtrctions plsm lipids monkeys