EFFECT OF CHLORPROMAZINE, RESERPINE, BENACTYZINE AND PHENOBARBITONE ON THE RELEASE OF CORTICOTROPHIN IN THE RAT

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1 Brit. J. Pharmacol. (1962), 19, EFFECT OF CHLORPROMAZNE, RESERPNE, BENACTYZNE AND PHENOBARBTONE ON THE RELEASE OF CORTCOTROPHN N THE RAT BY A. ASHFORD AND M. SHAPERO* From the Pharmacology Department, The Crookes Laboratories, Park Royal, London, N.W.1O (Received Jly 23, 1962) A single injection into the rat of chlorpromaine, reserpine, benactyine or phenobarbitone stimlates the release of corticotrophin. This effect is not seen after the drgs have been injected daily for 5 days, nor when the rats are hypophysectomied or pretreated with hydrocortisone. The stimlant effect of ether on corticotrophin release is not modified by pretreatment with a single injection, nor to any great extent after 5 daily injections of these drgs. t has been reported that central nervos system depressants may either depress or stimlate the pititary-adrenal axis, depending on the conditions nder which they are examined. Varios athors have claimed that both chlorpromaine and reserpine when administered alone (Van Peenen & Way, 1957; Mahfo & E, 1958), and after pentobarbitone (Sevy, Ohler & Weiner, 1957; Olling & de Wied, 1956), block the release of corticotrophin following a stress, bt do not themselves case a depletion of adrenal ascorbic acid. n contrast, Holbaer & Vogt (1954) showed that the chlorpromaine does not prevent the effects of operative stress and itself cases a depletion of adrenal ascorbic acid in the intact, non-stressed rat. Similarly reserpine (Wells, Briggs & Mnson, 1956) and morphine (Briggs & Mnson, 1955) indce corticotrophin release when given in single doses, the effect being lost when they are given daily for 5 days. t is now realied (Gant, Chart & Reni, 1961 ; Mnson, 1961) that many drgs case a secretion of corticotrophin from the pititary gland when first injected, and that their repeated administration leads to adaptation. We have investigated the action of chlorpromaine, reserpine, benactyine and sodim phenobarbitone on corticotrophin release in the rat, sing the depletion of adrenal ascorbic acid as an index of activity. The effect of one injection or several daily injections of these componds was stdied in intact rats, and in order to confirm that the effect observed is mediated throgh the pititary gland the drgs were also injected into hypophysectomied and into hydrocortisone-treated rats. Present address: Ward Blenkinsop & Co., Wembley, Middlesex.

2 DEPRESSANT DRUGS AND CORTCOTROPHN 459 METHODS Male albino rats weighing between 12 and 17 g were maintained for at least one week prior to se in a constant environment at a temperatre of 8 F. Test drgs were administered intraperitoneally in aqeos soltion, with the exception of reserpine which was administered as a sspension. The volme of injection was.5 ml./1 g body weight. Control animals received the dilent only. The stressing procedre consisted of ptting the rats into an ether chamber for 2.5 to 3 min, and was carried ot 1 hr before killing. At varios times after injection, as indicated in the tables, the adrenals were rapidly removed nder ether anaesthesia, trimmed free of fat, weighed, and homogenied in 2.5% metaphosphoric acid. The homogenate was centrifged and ascorbic acid was estimated in the centrifgate by the dichlorphenol indophenol dye method. Hydrocortisone acetate was injected as a 25 mg/ml. aqeos sspension, a first injection of 6 mg/ 1 g body weight being given intraperitoneally at 2 p.m. on the day previos to the experiment and a second similar injection at 9 a.m. the following day. Experimental drgs were given 3 hr later. Hypophysectomy was carried ot by the parapharyngeal approach 24 hr before the test and the hypophysectomied rats were 'given dextrose to drink overnight. The completeness of hypophysectomy was checked visally at the end of the experiment and the reslts from rats with a vestige of the pititary left were discarded. n Tables 1 and 2 the actions of the drgs in stressed and non-stressed animals are compared with their respective controls, and a comparison is also made between the effects of the drgs themselves in stressed and non-stressed rats. RESULTS ntact rats given single injections only. All the componds examined cased a depletion of adrenal ascorbic acid in the intact non-stressed rat (Table 1). The threshold dose for chlorpromaine was between 1.4 and 2.8 mg/kg. Ether also markedly depleted adrenal ascorbic acid. The possible effects which the central nervos system depressants may have on the depleting action of ether were obscred by their own stimlant effects on corticotrophin release. However, chlorpromaine at 1.4 mg/kg over a period of 2.5 hr and at 2.8 mg/kg over a period of 6 hr before killing did not inhibit the depletion cased by ether in spite of the fact that the drg itself is non-stimlant nder these conditions. n two cases, reserpine at.1 mg/kg and phenobarbitone at 5 mg/kg, the combination of drg and stress redced the adrenal ascorbic acid level to a significantly greater degree than stress alone. These lower levels of ascorbic acid represent in or experience the maximm possible depletion. ntact rats given daily injections for S days. The administration of chlorpromaine, reserpine, benactyine and sodim phenobarbitone daily for 5 days reslted in the loss of the ability to deplete adrenal ascorbic acid (Table 2). ndeed, the level of ascorbic acid was significantly increased over that of the controls in the grops treated with reserpine (.5 mg/kg) and phenobarbitone. However, the stressing action of ether was still mainly naffected by drg treatment, althogh there were indications that chlorpromaine at 2.8 mg/kg, reserpine at.5 mg/kg and phenobarbitone at 5 mg/kg antagonied it to some extent. Hydrocortisone-treated rats and hypophysectomied rats. The depleting effect of the experimental drgs on adrenal ascorbic acid was abolished both by pretreatment with hydrocortisone acetate and by hypophysectomy (Table 3). Q

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5 462 A. ASHFORD and M. SHAPERO DSCUSSON Chlorpromaine, reserpine, benactyine and phenobarbitone cased a fall in the adrenal ascorbic acid level of intact rats. Since this action was abolished by hypophysectomy, it is reasonable to assme that the drgs stimlate the release of corticotrophin from the anterior pititary gland and do not affect the adrenal cortex directly. Hydrocortisone inhibits the release of corticotrophin from the pititary gland (Sydnor, 1955) by a feedback mechanism and may act at the level, of the hypothalams since plasma from the hypothalamico-hypophyseal portal vessels of the dog will still case a depletion of adrenal ascorbic acid when injected into the hydrocortisone-blocked rat (Porter & Jones, 1956). Since pretreatment with hydrocortisone blocked the stressing action of all the componds which we examined, it is probable that they do not act directly on the pititary gland bt at some point earlier, possibly on the hypothalams. Daily administration of the drgs for 5 days led to a loss of the ability to release corticotrophin, an effect which is similar to that reported by Wells et a. (1956) for reserpine and by Briggs & Mnson (1955) for morphine. However, repeated injections of the drgs sed in this investigation did not block the stressing effect of ether, althogh chlorpromaine, reserpine and phenobarbitone significantly redced it in some experiments. This finding is not in complete agreement with those of the above-mentioned workers, who showed that, after 5 days of treatment, morphine blocked the effects of histamine, and reserpine blocked the effects of ether on corticotrophin release. We also failed to show any inhibition of ether stress by the central nervos system depressant drgs after their initial injection, althogh this may well have been de to or choice of conditions nder which each depressant agent acted as a stress in itself. However, chlorpromaine in the two instances in which it did not case adrenal ascorbic acid depletion still failed to block ether. Maickel, Westermann & Brodie (1961) and Saffran & Vogt (196) showed that reserpine lowers the corticotrophin content of the pititary gland and prevents (Maickel et al., 1961) the release of corticotrophin when the rats are exposed to cold 2 hr later. Conversely, the stressing effect of reserpine on corticotrophin release is blocked by an initial exposre to cold when reserpine is given 2 hr later. t was sggested that the depletion of corticotrophin in the pititary gland cased by the first stimls was responsible for the failre of the second stimls to evoke a stress reponse (Maickel et al., 1961). This sggestion cannot explain the tolerance that developed toward chlorpromaine, benactyine, reserpine and phenobarbitone after they have been injected repeatedly, since, on the 5th day of treatment, ether still evoked a discharge of corticotrophin. Presmably the level of corticotrophin in the pititary had risen sfficiently by this time, in spite of contined drg treatment, to case a depletion of adrenal ascorbic acid on discharge. The fact that hydrocortisone blocked the stressing action of ether may mean that ether was also acting throgh the hypothalams.

6 DEPRESSANT DRUGS AND CORTCOTROPHN 463 The initial stressing action of phenobarbitone is of interest in view of the fact that barbitrates are generally thoght to depress corticotrophin release withot first stimlating (Gant et al., 1961). REFERENCES BRGGS, F. N. & MUNSON, P. L. (1955). Stdies on the mechanism of stimlation of A.C.T.H. secretion with the aid of morphine as a blocking agent. Endocrinol., 57, GAUNT, R., CHART, J. J. & RENZ, A. A. (1961). Endocrine pharmacology. Science, 133, HOLZBAUER, M. & VOGT, M. (1954). The action of chlorpromaine in diencephalic sympathetic activity and on the release of adrenocorticotrophic hormone. Brit. J. Pharmacol., 9, MAHFOUZ, M. & E, E. A. (1958). The effect of reserpine and chlorpromaine on the response of the rat to acte stress. J. Pharmacol. exp. Ther., 123, MACKEL, R. P., WESTERMANN, E.. & BRODE, B. B. (1961). Effects of reserpine and cold exposre on pititary-adrenocortical fnction in rats. J. Pharmacol. exp. Ther., 134, MUNSON, P. L. (1961). Endocrine pharmacology. Selected topics, hypothalamic secretory factor for A.C.T.H. Ann. Rev. Pharmacol., 1, OLLNG, C. C. J. & DE WED, D. (1956). nhibition of the release of corticotrophin from the hypophysis by chlorpromaine. Acta Endocrinol., 22, PORTER, J. C. & JoNEs, J. C. (1956). Effect of plasma from hypophyseal-portal vessel blood on adrenal ascorbic acid. Endocrinol., 58, SAFFRAN, M. & VOGT, M. (196). Depletion of pititary corticotrophin by reserpine and by a nitrogen mstard. Brit. J. Pharmacol., 15, SEVY, R. W., OHLER, E. A. & WENER, A. (1957). Effect of chlorpromaine on stress-indced adrenal ascorbic acid depletion. Endocrinol., 61, SYDNOR, K. L. (1955). Blood A.C.T.H. in the stressed adrenalectomied rat after intravenos injection of hydrocortisone. Endocrinol., 56, VAN PEENEN, P. F. D. & LEONG WAY, E. (1957). The effect of certain central nervos system depressants on pititary-adrenal activating agents. J. Pharmacol. exp. Ther., 12, WELLS, H., BRGGS, F. N. & MUNSON, P. L. (1956). The inhibitory effect of reserpine on A.C.T.H. secretion in response to stressfl stimli. Endocrinol., 59,