Analogs of luteinizing hormone-releasing hormone with increased biological activity produced by D-amino acid substitutions in position 6

The incorporation of simple d-amino acids in place of glycine in position 6 of the LH-RH decapeptide produces analogs which have far greater gonadotropin-releasing activities in vivo and in vitro than the natural hormone. An investigation of the structural features of the d-amino acids responsible for this phenomenon suggests that an increase in the lipophilic character and perhaps the size and aromaticity of the side chain coincides with an increase in biological activity. This is demonstrated by the LH-releasing activities of the following series of peptides which were assayed over a period of 6 h in immature male rats: [d-Glu(6)]-,1.8;[d-Ala(6)]-,7.0;[d-Leu(6)]-,9,0;[d-Phe(6)]-,10;[d-Trp(6)]-LH-RH, 13 times more active than LH-RH itself. In contrast to previous results with [d-Ala(6)]-and [d-Leu(6)]-LH-RH, where the substitution of an ethylamide group for the glycine amide at the C-terminus produces large increases in LH/FSH releasing activity, the ethylamide derivatives of [d-Phe(6)]-and [d-Trp(6)]-LH-RH were actually less potent than their parent peptides. [(N-Me-d-Ala)(6)]-LH-RH was found to be approximately 70 times less active than [d-Ala(6)]-LH-RH which indicates that disruption of a preferred receptor-site binding conformation might be brought about by methylation of the amide linkage in this position.

Inhibition of luteinizing hormone release by analogs of luteinizing hormone-releasing hormone (LHRH) in vitro

Sixteen synthetic analogs of LH-releasing hormone (LHRH) were tested for their ability to inhibit the stimulation of LH release induced by 3 X 10(-9)M LHRH in anterior pituitary cells in monolayer culture. Half-maximal inhibition of LHRH-induced LH release was obtained with 7 analogs at concentrations which ranged from 3 X 10(-6)M to 3 X 10(-5)M. None of these seven analogs had significant LH-releasing activity at concentrations up to 10-5M. Nine analogs had no detectable antagonistic activity when tested in up to a 3000-fold molar ratio of analog to LHRH.

Blockage of ovulation in rats by inhibitory analogs of luteinizing hormones-releasing hormone

An antagonist of luteinizing hormone-releasing hormone (LH-RH). [D-Phe2-Phe3-D-Phe6]-LH-RH (Phe, phenylalanine), suppressed luteinizing hormone (LH) and follicle-stimulating hormone (FSH) release in male rats in response to LH-RH for at least 4 hours. Three subcutaneous injection of 1 milligram of this antagonist into rats during proestrus completely suppressed ovulation, while a single injection of 1.5 milligrams per rat inhibited 95.3 percent of the preovulatory surge of LH, 84.2 percent of the FSH surge, and suppressed ovulation by 86.4 percent.

Inhibitory activity of analogues of luteinizing hormone-releasing hormone (LH-RH) in vitro and in vivo

Improved inhibitors of LH-RH are those which, beside removal of the histidine residue at position 2 of LH-RH, include replacement of glycine at position 6 by a D-amino acid. A still better modification is replacement of the histidine residue at position 2 by D-phenylalanine. As examples, when tested in pituitary cells in culture, [Des-His2]LH-RH, [Des-His2, D-Leu6]LH-RH, [Des-His2, D-Phe6]-LH-RH, [D-Phe2]LH-RH, [D-Phe2, D-Leu6]LH-RH and [D-Phe2, D-Phe6]LH-RH inhibit 50% of LH release induced by LH-RH at molar ratios (MR50S) of 3000, 500, 60, 1000, 150 and 25, respectively. [D-Phe2, D-Phe6, D-Phe7]LH-RH, [D-Phe2, Phe3, D-Phe6]LH-RH and [D-Phe2, Phe5, D-Phe6]LH-RH have MR50 values of respectively 400, 100, and 75. When evaluated in vivo, some of the mentioned structural modifications permit inhibition of LH-RH action at molar ratios lower than observed in vitro. At a 500 molar ratio, [D-Phe2, Phe5, D-Phe6]-LH-RH inhibits the plasma LH rise induced by LH-RH by 75% up to 5 h after its injection. When administered at 12.00 hours at the dose of 2 mg, this analogue inhibits the spontaneous pro-oestrus LH surge and ovulation by 85 and 75%, respectively.

Peptides readily penetrate the blood-brain barrier: uptake of peptides by synaptosomes is passive

The intracarotid artery quick injection technique of Oldendorf was utilized to determine the Brain Uptake Index (BUI) of radio-labeled peptides in comparison with 3H2O or 14C-antipyrine as counterlabels. The normalized BUI values for 3H-MIF-I, 3H-alpha-MSH and 14C-AVP were 13.7, 9.6 and 13.0 respectively at 15 sec after injection consistent with their having readily penetrated the blood-brain barrier. The BUI values were similar, though somewhat increased, at 10 min postinjection consistent with their ready exit across the blood-brain barrier. At 15 sec after injection 0.5+/-0.1%/g brain of the originally injected peptide label was recovered; and 0.1+/-0.2%/g brain was recovered after 10 min. The label was distributed uniformly in the major brain regions at both times. However, the percentage of the originally injected label/g of pineal and pituitary gland tissue was 10-20 X increased as compared with the major brain regions as would be expected by their location outside the blood-brain barrier. The in vitro uptake of the radio-labeled peptides by synaptosomes prepared from the whole brain and the major brain regions was passive; it was not temperature dependent, nor was it Na+ dependent. However, the binding of the three peptides by the synaptosomes varied considerably: AVP greater than MSH greater MIF: 50 greater than 5 greater 1. The penetratin of the blood-brain barrier by the three peptides is consistent with their having CNS effects.

Distribution of 3H-alpha-MSH in rat brain

Radioactive synthetic alpha-MSH, prepared by selective tritiation of its dibromo-L-tyrosine-derivative, was injected into the carotid artery of intact, hypophysectomized or pinealectomized rats. More radioactivity was found in the occipital cortex, cerebellum, and pons-medulla than in most other brain parts of rats decapitated 15 sec and, to a less significant extent, 30 min after injection. Part of this radioactivity behaved like alpha-MSH in several identification procedures. After administration of 3H-tyrosine, the least radioactivity was consistently found in the pons-medulla. Large amounts of radioactivity after 3H-alpha-MSH were found in the pituitary and, particularly in the hypophysectomized rats, in the pineal. The half-time disappearance of the first component of radioactivity from the blood of each group of rats injected with tritiated-alpha-MSH was no more than 2.5 minutes, a time considerably shorter than the behavioral and EEG effects of this pituitary hormone on visual attention.

Comparison of the anti-LH/FSH-RH and anti-ovulatory activities of (D-Phe2, D-Leu6)-LH-RH and (D-Phe2, D-Ala6)-LH-RH

The anti-LH/FSH-RH and antiovulatory activities of [D-Phe2, D-Leu6]-LH-RH and [D-Phe2, D-Ala6]-LH-RH were compared in rats. Both peptides inhibited the LH and FSH release induced by LH-RH in immature male rats, but, 4 hr after the injection, [D-Phe2, D-Leu6]-LH-RH still suppressed the LH and FSH release whereas the [D-Phe2, D-Ala6]-LH-RH did not. When the peptides were administered in equal doses on the afternoon of the day of proestrus in 4-day cycling rats, [D-Phe2, D-Leu6]-LH-RH more completely inhibited the ovulation occurring on the following morning than [D-Phe2, D-Ala6]-LH-RH. Thus, the incorporation of D-Leucine into position six of the decapeptide chain gives a more potent inhibitor than that resulting from the insertion of D-Alanine.

Inhibition by six somatostatin analogs of plasma growth hormone levels stimulated by thiamylal and morphine in the rat

Administration of sodium thiamylal (50 mg/kg,i.p.) and morphine (3 mg/animal,s.c.) leads to high plasma levels of growth hormone (GH) with a maximum measured approximately 30 min after injection. When the same dose of morphine is administered 60 and 120 min later and small additional doses of thiamylal are injected to maintain the animals deeply anesthetized, constant high levels of plasma GH are maintained up to the last interval studied (3 h). This in vivo model has been used to evaluate the potency and duration of action of somatostatin and of six of its analogs by serial blood sampling of animals bearing a cannula inserted into the right superior vena cava. A significant inhibitory effect of somatostatin (45% inhibition) is observed 15 min after a s.c. injection of 1 mug of the peptide while a near maximal effect (90-95% inhibition) is found at a dose of 25 mug. Both the degree of inhibition and duration of action of somatostatin are dose-dependent. Inhibitory activities equivalent to 1-250 mug of somatostatin can be measured with the model described. [Tyr1] somatostatin, [D-Ala1]somatostatin, [N-acetyl-Cys3] somatostatin and [N-benzoyl-Cys3] somatostatin have activities indistinguishable from somatostatin itself while [D-Lys4] somatostatin and [des-amino1, des-carboxy14] somatostatin have approximately 10% the activity of the natural hypothalamic peptide. This in vivo model offers advantageous characteristics of precision and reproducibility for the evaluation of potency of inhibitors of GH release.

Stimulation of luteinising hormone (L.H.) release after oral administration of an analogue of L.H. releasing hormone

An analogue of luteinising-hormone-releasing hormone ([D-Leu-6, desGly-NH2-10]-L.H.R.H.-ethylamide) was administered by mouth to thirteen healthy men. In eight men 10 mg of this superactive L.H.R.H. analogue significantly increased mean plasma-L.H. within 45 minutes of administration. This increase was sustained for more than 5 hours. 2 mg of the analogue did not significantly increase plasma-gonadotrophin concentrations in the five men to whom this smaller dose was given. Oral administration of some L.H.R.H. analogues would seem to be effective in releasing L.H. in man.

Increased and prolonged LH-RH/FSH-RH activity of synthetic (D-Ala6, Des-Gly-NH210)-LH-RH-ethylamide in normal women

A synthetic LH-RH analogue (D-Ala6, Des-Gly-NH210)-LH-RH ethylamide exhibited an increased and prolonged LH-RH/FSH-RH activity in normal women. The integrated amounts of LH and FSH levels for this LH-RH analogue were about nine and five times greater than for the same doses of synthetic LH-RH. It is expected that this synthetic LH-RH analogue might yield more positive results than with LH-RH when used in infertility problems.

Gonadotropin-releasing activity of two highly active and long-acting analogs of luteinizing hormone-releasing hormone after subcutaneous, intravaginal, and oral administration

The gonadotropin-releasing activities of two synthetic analogs of luteinizing hormone-releasing hormone (LH-RH), D-Ala6-des-Gly10-LH-RH ethylamide and D-Leu6-des-Gly10-LH-RH ethylamide were evaluated in immature female rats after subcutaneous, intravaginal, and oral administration. Maximal peaks of serum LH and follicle-stimulating hormone (FSH) levels after administration of both analogs by any of the three routes were obtained at 2 hours. Therefore, serum gonadotropin levels declined slowly, so that at 6 hours LH levels had returned to base line values, whereas FSH levels remained elevated for up to 10 hours. The integrated serum gaondotropin levels after LH-RH and both analogs over a 10-hour period indicated that D-Leu6-des-Gly10-LH-RH EA and D-Ala6-des-Gly10-LH-RH EA released more LH and FSH than did the LH-RH decapeptide. The intense and long-acting properties of these analogs in releasing LH and FSH suggest the possibility that they may be more useful therapeutically than LH-RH.

Synthesis and biological properties of the 2-L-beta-(pyrazolyl-1)alanine analogs of luteinizing hormone-releasing hormone and thyrotropin-releasing hormone

The luteinizing hormone-releasing hormone (LH-RH) analog, less thanGlu-Pyr(1)Ala-Trp-Ser-Tyr-Gly-Leu-Arg-Pro-Gly-NH2, and the thyrotropin-releasing hormone (TRH) analog, less thanGlu-Pyr(1)Ala-Pro-NH2, were synthesized by azide couplings of the dipeptide hydrazide, less thanGlu-Pyr(1)Ala-NHNH2, to the C-terminal octapeptide of LH-RH and to proline amide, respectively. In an ovariectomized, steroid-blocked rat assay, the LH-RH analog was found to have only 1% of the LH-releasing activity of the natural hormone. The TRH analog was 1.5 times more effective than TRH itself in releasing TSH in vivo from the anterior pituitary of mice. This peptide is one of two synthetic peptides so far discovered which are more potent than TRH.

Inhibitory activity of four analogs of luteinizing hormone-releasing hormone in vivo

Four analogs of luteinizing hormone-releasing hormone (LH-RH), [des-His2,D-Ala6]-LH-RH, [des-His2,D-Ala6, des-Gly-NH2(10)1-LH-RH ethylamide, [des-His2,D-Leu6]-LH-RH, and [D-Phe2,D-Leu6]-LH-RH, at 300-fold molar ratios (analog/LH-RH) led to an almost complete inhibition of LH response to LH-RH in anesthetized 4-day cycling rats on the afternoon of proestrus. At a 75-fold molar ratio, [des-His2,D-Ala6]-LH-RH still inhibited the LH-RH-induced LH release by 50%. The ethylamide substitution at the COOH terminus of [des-His2,D-Ala6]-LH-RH did not significantly improve the inhibitory activity of the molecule.

Hypothalamic hormone interaction in acromegaly

The growth hormone response to the administration of the currently available synthetic hypothalamic hormones was assessed in eleven patients with acromegaly. Eight of them showed a positive GH response to thyrotrophin releasing hormone and three showed no response. The GH response to TRH was shown to be unrelated to the thyrotrophin response to TRH. The GH response to TRH was inhibited by the administration of growth hormone release inhibiting hormone. Luteinizing hormone/follicle stimulating hormone releasing hormone (LHRH) caused a positive GH response in four patients, but this was trivial in three. The TRH mediated GH release in acromegaly is not mediated via TSH and appears to be attributable to loss of specificity of the receptor sites on the somatotroph to the hypothalamic hormones.

Growth hormone release inhibiting hormone: actions on thyrotrophin and prolactin secretion after thyrotrophinreleasing hormone

The hypothalamic tetradecapeptide growth hormone release inhibiting hormone (GH-RIH) blocked the thyrotrophin response to thyrotrophin-releasing hormone (TRH) in normal people and in patients with primary hypothyroidism. This inhibition was dose related. The TRH-induced prolactin release was not affected by GH-RIH. This dissociation of the thyrotrophin and prolactin responses to TRH by GH-RIH suggests that there are different mechanisms for release of thyrotrophin and prolactin and that only the former is affected by GH-RIH.

Attempts to programme ovulation with exogenous oestrogens and LH-RH analogue

An attempt was made to programme ovulation in women on a predetermined day of the menstrual cycle by treatment used to induce ovulation in anovulatory sterility. At laparotomy for elective sterilization the ovaries were observed to assess the occurrence of ruptured follicles and ovulation. Histological analysis of ovaries and endometrium was performed, and ova were recovered from some women. Several regimens were tested but ovulation seldom occurred as planned. Clomiphene citrate, human chorionic gonadotrophin (HCG), synthetic luteinizing hormone releasing hormone (LH-RH), and ethinyloestradiol were ineffective. Human menopausal gonadotrophin followed by HCG was more effective, but multiple ovulations occurred. When one single injection of a potent long-acting LH-RH analogue was given on day 13 of the cycle to 10 women pretreated with ethinyloestradiol signs of recent ovulation were observed on day 15 in seven and on day 16 in two.

Anti-luteinizing (LH)-releasing activity of several analogues of LH-releasing hormone

The anti-LH-releasing activity of several analogues of LH-RH was tested by 2-hour infusion in ovariectomized, estrogen-progesterone-pretreated rats and in immature male rats. [Leu3]LH-RH, [Leu3, desGly10]-LH-RH ethylamide, [desHis2, Leu3,desGly10]-LH-RH ethylamide, [Gly2, Leu3,desGly10]-LH-RH ethylamide, [Leu1, desGly10]-LH-RH ethylamides, [desHis2,D-Ala6,desGly10]-LH-RH ethylamide, [desHis2,Leu3,D-Ala6, desGly10]-LH-RH ethylamide, and [D-pGlu1,desGly10]-LH-RH ethylamide, and and [D-pGlu1,desHis2,desGly10]-LH-RH ethylamide showed some anti-LH-releasing activity, but never completely inhibited the increase in serum LH in response to LH-RH. No significant differences were found among the analogues tested and [desHis2,desGly10]-LH-RH ethylamide, and inhibitory potency was not improved with those peptides containing D-alanine in position 6 of the chain. None of the analogues tested, including [desHis2,desGly10]-LH-RH ethylamide, was able to block the LH-RH-induced FSH release in these systems.

Polyfluoroalkylamine derivatives of luteinizing hormone-releasing hormone

A series of C-terminally fluorinated analogs of luteinizing hormone-releasing hormone (LH-RH) was synthesized by a combination of solid-phase and classical techniques and found to have interesting properties when assayed for LH- and FSH-releasing activities over a prolonged period of time in immature male rats. One of the peptides, desGly-10-LH-RH-2,2,2-trifluoroethylamide, was found to be about nine times more effective than LH-RH in releasing LH, or approximately twice as active as the corresponding alkylamide peptide, desGly-10-LH-RH-ethylamide. However, desGly-10-LH-RH-2,2,3,3,3-pentafluoropropylamide was only slightly more active than LH-RH and considerably less active than the corresponding propylamide analog. A family of peptides was also prepared containing D-alanine in position six of the chain in conjunction with the C-terminal modifications. D-Ala-6,desGly-10-LH-RH-2,2,2-trifluoroethylamide, surprisingly, gave patterns of gonadotropin release which were only as intense and virtually identical with those obtained with D-Ala-6,desGly-10-LH-RH-ethylamide which in turn releases about 20 times more LH than a similar dose of LH-RH. D-Ala-6,desGly-10-LH-RH-propylamide also gave almost identical patterns of gonadotropin release. D-Ala-6,desGly-10,LH-RH-2,2,3,3,3-pentafluoropropylamide was considerably less potent, being only five times more effective than LH-RH.

An in vivo assay for anti-LH-RH and anti-FSH-RH activity of inhibitory analogues of LH-RH

A convenient and sensitive method for testing anti-LH- and FSH-releasing activities of antagonists of LH-RH was devised. The peptides to be tested were injected subcutaneously together with synthetic LH-releasing hormone (LH-RH) in immature male rats. Serum LH and FSH concentrations were measured 30 min later by radioimmunoassay. In this system, [DesHis2]-LH-RH failed to block the pituitary response to LH-RH in agreement with previous data. The administration of [DesHis2, desGly10]-LH-RH ethylamide, [Des-His2, Leu3, des Gly10]-LH-RH ethylamide, [Des-His2, D-Ala6, des-Gly10]-LH-RH ethylamide, and [DESHis2, D-Ala6]-LH-RH in doses of 200 mug/rat, and [DesHis2, Leu3, D-Ala, desGly10]-LH-RH ethylamide in doses ranging from 100-400 mug/rat caused a significant inhibition of LH-RH-induced release of LH and FSH. On the other hand, [DesHis2, desGly10]-LH-RH propylamide, and [Leu2, Leu3, D-Ala6, desGly10]-LH-RH ethylamide failed to block the response to LH-RH. Among the peptides tested, [DesHis2, d-ala6, desGly10]-LH-RH etylamide, [Leu2, Leu3, D-Ala, desGly10]-LH-RH ethylamide in doses of 200 mug and [DesHis2, Leu3, D-Ala6, desGly10]-LH-RH ethylamide in a dose of 400 mug/rat showed some intrinsic LH and FSH-releasing activities. The method described here is simple and convenient for studying the anti-LH-RH release activity of inhibitory analogues of LH-RH, and also enabled us to demonstrate for the first time an in vivo inhibition of FSH release by these analogues.

Synthesis and biological activity of LH-RH analogs modified at the carboxyl terminus

Des(Pro9,Gly10)-LH-RH ethylamide, des(Pro9,Gly10)-LH-RH butylamide, desGly10-LH-RH 2-aminoethylamide, and desGly10-LH-RH hydrazide were synthesized by a solid-phase method involving cleavage of protected peptide intermediates from their resin support by reaction with ethylamine, butylamine, ethylenediamine, and hydrazine, respectively. In the assay utilizing steroid pretreated, ovariectomized rats, the peptides were found to have the following LH-releasing activities when compared with natural LH-RH: ethylamide, 0.2%; butylamide, 0,1%; 2-aminoethylamide, 2.4%; hydrazide, 12%. DesGly10-LH-RH hydrazide was used as a precursor in the synthesis of desGly10-LH-RH allylamide and desGly10-LH-RH propargylamide by conversion to the azide and reaction with allylamine and propargylamine, respectively. LH and FSH levels were measured over a 4-hr period after subcutaneous injection of these two peptides into immature male rats in order to detect any prolongation of activity. The allylamide analog was quite active, releasing 1.7 times more LH and 1.3 times more FSH than the same dose of LH-RH. The propargylamide analog was considerably less active, exhibiting 50% LH-releasing activity and 64% FSH-releasing activity. Neither peptide appeared to be longer acting than LH-RH.

Radioimmunoassay for GH-release inhibiting hormone

The synthetic growth hormone release inhibiting hormone (GH-RIH) was conjugated with human serum globulin using glutaraldehyde and administered to rabbits. An antiserum thus generated 70% of 125I-Tyr1-GH-RIH. The binding was inhibited by unlabelled GH-RIH and the inhibition was dose-related, enabling us to establish a radioimmunoassay method for GH-RIH. The minimum detectable dose was 4 pg. A linearity was demonstrated for immunoreactive GH-RIH of extracts of rat and pig hypothalami, indicating that they contained substance(s) indistinguishable from GH-RIH. Various hypothalamic and pituitary hormones did not interfere with the radioimmunoassay, but considerable cross-reaction was observed for linear GH-RIH and the ring portion of GIH-RIH, suggesting that the antigenic determinant involved the amino acid sequence from position 3-14 of GH-RIH or part of it. Plasma protein appears to contain substance(s) immunologically indistinguishable from GH-RIH or to interfere, in a nonspecific manner, with the radioimmunoassay system for GH-RIH.

Distribution of radioactivity in the organs of the rat and mouse after injection of L-(3H)prolyl-L-leucyl-glycinamide

The distribution of radioactivity after intrajugular injection of L-(3H)-prolyl-L-leucyl-glycinamide has been studied by whole-body autoradiography in the mouse and by direct measurement of radioactivity in individual organs of the rat. There is good agreement between results obtained with the two techniques and animal species. High levels of radioactivity were found in the pineal gland, anterior pituitary, posterior (including intermediate) lobe of the pituitary, and epididymal and brown fat. Lower uptake of radioactivity occurred in the submaxillary gland, kidney, and adrenal gland. The preferential uptake of radioactivity by the pineal gland after injection of the labelled tripeptide suggests a role for this hypothalamic hormone in the control of pineal activity.

The antigenic determinant of the LH-releasing hormone for three different antisera

Antigenic determinants of LH-releasing hormone (LH-RH) were investigated by testing the cross-reaction of LH-RH analogues and fragments in LH-RH radioimmunoassay (RIA) systems using 3 different antisera against the LH-RH decapeptide. Rabbit antiserum No. 419 was generated against LH-RH adsorbed on polyvinylpyrrolidone (PVP). Antisera Nos. 710 and 742 were produced by immunizing rabbits with LH-RH conjugated either with bovine serum albumin through its C-terminus, or with human serum albumin through the N-terminus, respectively. For antiserum No. 419, the N-terminal (pyro)-glutamic acid and/or histidine in positions 1 and 2 of LH-RH, respectively, were found to enhance the antigen-antibody interaction, but were not indispensable for it. Similarly, the C-terminal amide and glycine-NH2 did not play a major role in these interactions. The LH-RH heptapeptide fragment, corresponding to amino acid sequence from positions 3 to 9, showed a cross-reactivity in this RIA system with LH-RH, although greater amounts than those of cold LH-RH were required for a comparable inhibition of binding of labelled LH-RH. For antiserum No. 710, the LH-RH hexapeptide fragment corresponding to positions 2 to 7 showed considerable cross-reactivity. Histidine in position 2 played an important role but neither the amide group nor the glycine amide group at the C-terminus were essential. For antiserum No. 742, the C-terminal tetrapeptide-amide fragment of LH-RH showed considerable cross-reactivity in the LH-RH, the amide moiety itself being of crucial importance. These antisera may be useful in investigating peptides related to LH-RH in biological materials.

Long-term infusion of growth hormone release inhibiting hormone in acromegaly: effects on pituitary and pancreatic hormones

Growth hormone release inhibiting hormone (GH-RIH) was infused at a rate of 1.3 mug/min for 28 hours into four patients with acromegaly, two of whom also had clinical diabetes mellitus. Growth hormone and glucagon were suppressed throughout the infusion though delayed secretion of insulin occurred in association with both meals and an oral glucose load. Glucose tolerance was improved in one diabetic patient who was taking chlorpropamide while the other required much less insulin than usual. Secretion of endogenous thyroid-stimulating hormone was lowered in one euthyroid patient on carbimazole. Luteinizing hormone, follicle-stimulating hormone, ACTH, and prolactin were not affected. Serum somatomedin levels were reduced in one patient. There was a rapid rebound of all the suppressed hormones when the infusions stopped. Longer-acting analogues of GH-RIH will be needed before long-term therapy of acromegaly or diabetes mellitus becomes possible, but such preparations should be available soon for clinical trial.

Growth hormone release inhibiting hormone in acromegaly

Growth hormone release inhibiting hormone (GHRIH) was administered by constant infusion over 75 minutes to eight acromegalic patients at different doses. 100 to 1,000 mug were equally effective in reducing circulating growth hormone (GH) levels; 25 mug lowered GH levels in only five patients, and at this dose the extent of the fall was smaller than from doses of 100 mug or more. 10 mug was ineffective. Injection of single doses of 500 mug by intravenous, subcutaneous, and intramuscular routes caused only small and transient reductions in GH levels, though the effect was improved by injecting the hormone intramuscularly in 2 ml of 16% gelatin. Injection of a suspension of 4 mg GHRIH in 1 ml of arachis oil lowered growth hormone levels for between three and four hours.In four acromegalic patients an oral 50-g glucose tolerance test was performed during a continuous infusion of either saline or 1,000 mug GHRIH. The "paradoxical" rise in growth hormone seen in these patients during the saline infusion was suppressed by GHRIH. The blood glucose responses were, moreover, modified by GHRIH in that the peak was delayed and occurred at the end of the infusion in each case. A "normal" glucose tolerance curve was converted to a "diabetic" type of response in two patients. This effect could be accounted for by the inhibition of insulin secretion known to occur with large doses of GHRIH.We speculate that acromegaly may be primarily a hypothalmic disease due to deficiency of GHRIH resulting in excessive secretion of growth hormone from the pituitary and adenoma formation due to inappropriate and prolonged stimulation of the pituitary.