Effect of L-5-HTP on the Release of Growth Hormone, TSH and Insulin

Endocrinol. Japon. 1973, 20 (2), 135,-441 Effect of L-5-HTP on the Release of Growth Hormone, TSH and Insulin MANABU YOSHIMURA, YUKIO OCHI, TADAYOSHI MIYAZAKI, KATSUHIKO SHIOMI AND TAKASHI HACHIYA 2nd Department of Internal Medicine, Kyoto Prefectural University of Medicine, Kyoto Synopsis Effect of L-5-HTP (L-5-hydroxytryptophane) on the release of human growth hormone (HGH), thyroid stimulating hormone (TSH) and immunoreactive insulin (IRI) was investigated in 7 normal subjects and 25 patients with endocrine disorders. A single oral dose of 200mg of L-5-HTP showed the elevation of HGH in plasma; however, no release of TSH and insulin in plasma of normal subjects. HGH response to L-5-HTP administration was less in quantity as compared with HGH respone to insulin hypoglycemia or arginine infusion. The timing of HGH respone to L-5- HTP was quite variable (between 30 and 120min) in an oral dose of L-5-HTP. No release of HGH by L-5-HTP administration was observed in each of the patients with primodial dwarfism, panhypopituitarism, pituitary dwarfism, and some cases of hypothyroidism. The effect of hyperglycemia or sedative on the release of HGH induced by L-5-HTP was observed. HGH release by L-5-HTP was not observed in these treatments of glucose or diazepam, therefore it might suggest that HGH release by L-5-HTP was inhibited by hyperglycemia or diazepam administration. Suppression of TSH release by L-5-HTP dose was noticed in some patients with hypothyroidism; however no effect in normal subjects. Neither elevation nor reduction of IRI was observed by the L-5-HTP oral dose in normal subjects. These findings suggested that L-5-HTP might induce the release of HGH from normal pituitary gland, that the release of TSH might be reduced by the dose of L-5-HTP in the patients with hypothyroidism, but not in normal subjects, and that IRI was not affected by the dose of L-5-HTP in normal subjects. The interaction between neurotransmitter and hormone from the pituitary gland has been investigated recently by the development of histochemical fluorescence method for the cellular demonstration of 5-hydroxytryptamine (serotonin). The varicosities of monoaminecontaining fibers showed a marked accumulation of catecholamines or serotonin at various parts of the hypothalmus by the fluorescence method. Possible involvement of serotoninergic neural elements in pituitary regulation has been stimulated by the demonstration of serotonin-containing neurons in the brain (Dahlstrom and Fuxe, 1964). The recent Received for publication February 23, 1973. studies indicated that dopamine caused the discharge of hypothalamic releasing hormones which in turn controlled the release of anterior pituitary hormones (Miiller et al., 1970; Kamberi et al., 1971a). However, the study about the effect of serotonin on the release of anterior pituitary hormone is not prevalent at present. Serotonin can not pass through the blood brain barrier. However L-5-hydroxytryptophane (L-5-HTP) can pass through it and it can be also infiltrate into the brain easily. L-5-HTP has been used for the treatment of depression and parkinsonism clinically (Fujiwara et al., 1971; Sano, 1972). And there are also several reports on the effect of L-5-HTP

YOSHIMURA et al. Endocrinol. April 1973 Japon. or serotonin on the release of some pituitary hormones or other hormones of humans. Therefore, the present study was designed to evaluate the effect of serotonin on the release human growth hormone (HGH), human thyroid stimulating hormone (TSH) and insulin using L-5-HTP. Materials and Methods Seven healthy volunteers, six males and one female, and twenty five patients with endocrine disorders were investigated. A single orai dose of 200mg L-5-HTP capsules, (Kyowa Hakko Kogyo Co., Ltd.), was given to the normal subjects and patients in the early morning, following an overnight fast. Regular insulin, 0.1 Unit per kg body weight, iv and 10 arginine solution (Eiken Kagaku Co. Ltd.) by iv drip, 0.5mg per kg body weight, were administered to the subjects and patients who were given L-5-HTP orally on another day. Blood samples were drawn at half an hour intervals from 10min before to 180min after the oral administration. HGH was measured by double antibody radioimmunoassay using the Wilhelmi HGH as a standard (Boden and Soeldner, 1967), and human TSH by double antibody radioimmunoassay using NIH TSH as a standard (Odell et al., 1965). Immuno-reactive insulin (IRI) was measured by double antibody radioimmunoassay using Novo insulin as a standard (Morgan and Lazarow, 1963). To investigate the effect of hyperglycemia on the release of HGH induced by L-5-HTP, a dose of 50gm glucose was given immediately before L-5- HTP administration. With each blood sample, blood glucose was measured with an autoanalyser (Hoffman, 1937). To find the effect of sedative on the release of HGH, diazepam (Yamanouchi Pharmaceutical Co., Ltd.) 6mg per day was given orally for 7 days, and on the 8th day, next morning after the last administra. tion of diazepam, L-5-HTP was given for HGH measurement. Results Figure 1 shows the level of HGH in plasma observed before and after a single oral dose of 200mg L-5-HTP. A rise attributable to L-5-HTP was observed in all normal subjects. The timing of HGH response was quite variable (between 30 and 120min) in an oral dose of L-5-HTP and a rise in plasma HGH was 7.0-18.8mƒÊg/ml in the maximum values. Plasma HGH levels in response to L-5-HTP were compared with those in response to arginine infusion and insulin-induced hypoglycemia in each of normal subjects and 5-HTP 0.2gm Orally Fig. 1. Effect of L-5-HTP on plasma HGH levels. Effect of L-5-HTP administration on HGH release was evaluated in seven normal subjects in the fasting state. Dotted marks show the normal range.

Vol.20, No.2 EFFECT OF L-5-HTP ON GH, TSH AND IRI after Insulin(x) or Arginine( E) (mug/ml) Fig. 2 Correlation between L-5-HTP and insulin or arginine. Maximum release of HGH (peak HGH) in three different stimulators was investigated in normal subjects and patients with endocrine disorders. Correlation between peak HGH levels by L-5-HTP and peak HGH by arginine or insulin was depicted in this figure. Peak HGH by L-5- HTP was less than peak HGH by arginine or insulin. Solid line represents the 45 degree line. patients. The peak HGH level (maximum value of HGH response) was used for comparison. Figure 2 shows the comparison between the peak HGH levels in response to L-5-HTP and to insulin-induced hypoglycemia or arginine. The peak HGH values induced by L-5-HTP administration were lower than these by insulin or arginine infusion. Table 1 indicates the plasma HGH levels in response to L-5-HTP and the peak HGH level in response to arginine or insulin in various endocrine disorders. Each of the patients with primodial dwarfism, pituitary dwarfism and panhypopituitarism and three of the four patients with primary hypothyroidism did not respond to L-5-HTP in HGH release. On the contrary, the four patients with hyperthyroidism and a patient with adrenogenital syndrome showed a rise in plasma HGH by the stimulation of L-5-HTP. There were some discrepancies in the response of HGH, where the subjects with primodial dwarfism and one of the four patients with primary hypothyroidism, who normally responded to arginine or insulin administration, did not respond to the oral dose of L-5-HTP. The effect of blood glucose or sedative on the HGH release stimulated by L-5-HTP was evaluated in normal subjects, as shown in Table 1. Effect of L-5-HTP on release of HGH in various endocrine disorders Max.=Maximum level of HGH.

YOSHIMURA et al. Endocrinol. April 1973 Japon. Table 2. Effect of glucose (50gm orally) or sedative (diazepam 6mg for a week) on release of HGH stimulated by L-5-HTP. Table 3. Effect of L-5-HTP on release of TSH in normal subjects and in the patients with primary hypothyroidism The patients with primary hypothyroidism (1, 2, 3) were not treated with thyroid drug. The patients with primary hypothyroidism (4, 5) were treated with 50ƒÊg triiodothyronine (Thyronamin, Takeda Pharmacutical Co. Ltd.) daily for two weeks. Table 2. Hyperglycemic state or diazepam inhibited the release of HGH induced by L-5-HTP. The effect of L-5-HTP on TSH release was investigated regarding seven normal subjects and five patients with primary hypothyroidism. No stimulation to TSH release was observed in normal subjects. However, suppression to TSH release was noticed in four of the five patients (Table 3). The changes of immunoreactive insulin(iri) levels were variable in normal subjects after the oral administration of L-5-HTP, as shown in Table 4. Blood glucose increased from 85.5 }5.6mg/dl to 97.0 }7.6mg/dl. Blood pressure did not fluctuate in all cases. As a side effect, nausea was observed in three out of thirty-two subjects after the oral administration of L-5-HTP. Discussion Brain catecholamines and indoleamines play an important role in controlling the release of releasing hormone from the hypothalamus (Frohman, 1972). The blockade of GH release induced by insulin-hypoglycemia was observed by reserpine, catecholamine and in-

Vol.20, No.2 EFFECT OF L-5-HTP ON GH, TSH AND IRI Table 4. Effect of L-5-HTP on release of IRI and HGH and on blood glucose in normal subjects (N=7) doleamine depletor (Muller et al., 1967a), and supposed to be due to the reduction of the amount of brain catecholamine and indoleamine by reserpine administration (Muller et al., 1967b). Reserpine induces the reduction of a large amount of serotonin, dopamine and noradrenaline from body deposits (Shore et al., 1956). On the contrary it has been reported by Muller et al., (1970) that the intraventricular injection of serotonin into the lateral ventricle of the rat brain had no effect on GH release. Concerning the other pituitary hormones, it was reported that serotonin had no effect on luteinizing hormone-releasing hormone (LH- RH) release from the hypothalmus in vitro incubation experiments (Schneider and Mc- Cann, 1969). The suppression of the release of follicle stimulating hormone-releasing hormone (FSH-RH) and prolactin-inhibiting hormone (PIH) was observed by the intraventricular administration of serotonin to the rat brain (Kamberi et al., 1971b). It was also reported that the subcutaneous injection of serotonin induced the enhanced production of corticosterone through ACTH secretion (Gromova et al., 1967). The animal experiments have given an outline of pharmacological action of serotonin. However a considerable disparity exists between the limited clinical studies available and works in animals. The lack of precise assay for the specific releasing hormones and the obscurity of species difference in the pharmacological action of serotonin leave these results tentative. In the present study the elevation of plasma HGH levels was observed by oral administration of L-5-HTP to normal human subjects. Recently, Feldman and Lebovitz (1972) reported on the increased level of HGH in patients with excessive serotonin secretion (carcinoid syndrome) and observed that the inhibition of serotonin release by serotonin antagonist (methysergide) restored HGH secretion toward normal. From these results, they suggested the stimulation of HGH release by serotonin. In the present study the amount of HGH release by L-5-HTP was less than that stimulated by insulin hypoglycemia or arginine infusion. HGH release in a patient with primodial dwarfism and some patients with hypothyroidism was not stimulated by L-5-HTP, although in these eases the plasma HGH levels were elevated by insulin hypoglycemia or arginine infusion. These findings suggest that a dose of 200mg L-5-HTP may not be enough to stimulatc HGH secretion in these subjects. The plasma TSH levels in normal subjects could not be influenced by the administration of L-5-HTP in the present study. However, in some patients with primary hypothyroidism

YOSHIMURA et al. Endocrinol. April 1973 Japon. TSH release was suppressed by L-5-HTP dose. The mechanism of the suppression to release TSH is not obscure in the present state, however additional survey are necessary to confirm and to analyse its mechanism. Concerning the effect of L-5-HTP on the release of hormone except HGH and TSH, insulin (IRI) was measured from the finding of elevated blood glucose by L-5-HTP. However, IRI was not affected by L-5-HTP in normal subjects. There were some observations that serotonin inhibited pancreatic insulin release in vivo and in vitro in animals (Quickel et al., 1971b) and in patients with diabetes mellitus (Quickel et al., 1971a, Feldman and Lebovitz, 1972), and did not inhibit insulin release in normal subjects. Nakai et al. (1972) reported that the plasma levels of ACTH and cortisol were increased significantly in normal subjects after the oral administration of 150mg L-5-HTP. Blood glucose after a single oral dose of L-5-HTP in a fasting state demonstrated an increase in the present study. As already reported L-dopa was effective to secrete HGH even after the intake of glucose (Boyd et al., 1970, Yoshimura et al., 1972). On the other hand, the oral administration of glucose blocked the release of HGH stimulated by the L-5-HTP dose. This finding indicates that HGH release by L-5-HTP was suppressed by the blood glucose level and it might suggest that HGH releasing mechanism by L-5-HTP differ from that of L-dopa. Concerning the effect of L-5-HTP on cardiovascular system, blood pressure and heart rate did not change significantly in all subjects. The experience of L-5-HTP in the treatment for patients with depression or parkinsonism has demonstrated the relative safety of this drug for the treatment (Fujiwara et al., 1971; Sano, 1972). The use of L-5-HTP as a clinical test for pituitary function appears quite attractive in view of its simplicity and minimal side effects. However, L-5-HTP administered orally has a limiting merit for the use of a diagnostic test of HGH release as a pituitary function test because of unpredictable timing of HGH response and of less reliability than arginine or insulin-induced hypoglycemia. The mechanism of GH release from the pituitary gland by the L-5-HTP dose is not clear at present. However, the possible involvement of serotoninergic agents in pituitary regulation will be further studied in the future. Acknowledgement We would like to appreciate Endocrinology Study Section, NIH, for supplying the materials of human TSH. References Boden, G. and J. S. Soeldner (1967). Diabetologia 3, 413. Boyd, A. E. III, H. E. Lebovitz and J. B. Pfeiffer (1970). New Engl. J. Med. 283, 1425. Dahlstrom, A. and K. Fuxe (1964). Acta Physiol. Scand. 62, Suppl. 232, 5. Feldman, J. M. and H. E. Lebovitz (1972). Program of IV Internat. Congress Endocrinology, abstract No. 87, p.35. Frohman, L. A. (1972). New Engl. J. Med. 286, 1391. Fujiwara, J., S. Otsuki, S. Sugiyama, Y. Nakajima, S. Watanabe and T. Suzuki (1971). Igakunoayumi 79, 367. (In Japanese) Gromova, E. A., M. Kraus and J. Krecek (1967). J. Endocrinol. 39, 345. Hoffman, W. S. (1937). J. Biol. Chem. 120, 51. Kamberi, I. A., R. S. Mical and J. C. Porter (1971a). Endocrinology 88, 1012. Kamberi, I. A., R. S. Mical and J. C. Porter (1971b). Ibid. 88, 1288. Morgan, C. R. and Lazarow A. (1962). Proc. Soc. Exp. Biol. Med. 110, 29. Muller, E. E., T. Saito, A. Arimura and A. V. Schally (1967a). Endocrinology 80, 109. Muller, E. E., S. Sawano, A. Arimura and

EFFECT O F L-5-HTP ON GH, TSH AND IRI A. V. Schally (1967b). Ibid. 80, 471. Muller, E. E., A. Pecile, M. Felici and D. Cocchi (1970). Ibid. 86, 1376. Nakai, Y., T. Yoshimi, H. Imura, Y. Yoshimoto and U. Moridera (1972). Folia Endocrinol. Japon. 47, 710 Abstract. (In Japanese) Qnickel, K. E. Jr., J. M. Feldman and H. E. Lebovitz (1971a). J. Clin. Endocr. Metab. 33, 877. Qnickel, K. E. Jr., J. M. Feldman and H. E. Lebovitz (1971b). Endocrinology 89, 1295. Sano, I. (1972). Folia Psychiat. Neurol. Jap. 26, 7. Schneider, H. P. G. and S. M. McCann (1969). Endocrinology 85, 121. Shore, P. A., S. L. Silver and B. B. Brodie (1956). Science 122, 284. Yoshimura, M., Y. Ochi, T. Miyazaki, K. Shiomi and T. Hachiya (1972). Endocrinol. Japon. 19, 543.