We have previously shown that LHRH agonist [D-Trp6,Pro9-NEt]LHRH (LHRHA) results in reversible oligozoospermia when given to normal subjects for up to ten weeks. A fall in plasma testosterone was accompanied by loss of libido and potency. We now report six subjects who were evaluated by semen analysis and hormone profile at two-week intervals during ten-week basal, 20-week treatment, and post-treatment periods lasting at least ten weeks. Treatment consisted of LHRHA (50 microgram subcutaneously daily), and testosterone enanthate (100 mg intramuscularly every two weeks). Sperm density (mean basal 76.7 +/- 8.7 x 10(6)/ml) fell consistently in each subject to a mean nadir of 12.3 +/- 4.5 x 10(6)/ml (p less than 0.001). This is similar to the mean nadir of 11.6 +/- 5.8 x 10(6)/ml achieved when LHRHA was given alone. In each individual subject, sperm density returned to his basal level after cessation of treatment. No consistent changes were seen in sperm motility of morphology, or in semen volume. Libido and potency were maintained in all subjects. An additional three subjects received testosterone enanthate alone in identical dosage for 20 weeks. No change in sperm density was observed. In contrast to treatment with LHRHA alone, combination treatment produces reversible oligozoospermia without attendant change in potency.

Adult↗

PubMedDate not supplied

Heterogeneity of sperm density profiles following 20-week therapy with high-dose LHRH analog plus testosterone.

Eight normal male volunteers received an LHRH analog, 100 to 500 micrograms daily, for 20 weeks. Testosterone enanthate, 100 mg, was given by injection every second week. Sperm density fell to 5.5 X 10(6)/ml and to 0 in two of the subjects receiving 100 micrograms, but was unchanged in the third. Three of the subjects who received 500 micrograms displayed azoospermia, whereas the other two showed no significant change in sperm density. The reasons for the heterogeneity are not clear. Only one of the three nonresponders had testosterone values that were higher than the other subjects. Gonadotropin levels were similar in responders and nonresponders. It is possible that the response to LHRH analog in man is determined by the extent of the reduction in LH bioactivity.

Adult↗

PubMedDate not supplied

Heterogeneity of sperm density profiles following 16-week therapy with continuous infusion of high-dose LHRH analog plus testosterone.

LHRH agonist analogs have been investigated as potential male contraceptives. It has been shown that the LHRH agonistic analog [D-Trp6,Pro9-NEt] LHRH (LHRHA) given to men in single doses up to 500 micrograms daily for up to 20 weeks with the coadministration of testosterone enanthate produces reversible oligozoospermia. Individual responses to the treatment, however, were variable. In this study, we gave the same analog to eight normal male volunteers as a continuous infusion of 500 micrograms daily for 16 weeks. Testosterone enanthate, 100 mg, was given by injection every second week. Six of the subjects became oligozoospermic but the other two retained sperm counts that were greater than 20 million/ml, although their treatment continued for 20 weeks. The reasons for this variability of response are not clear. Serum immunoreactive LH values increased during the infusion period whereas testosterone declined. FSH values fell during treatment in all subjects except the two non-responders. The acute pituitary response to LHRHA during the treatment or shortly thereafter (48 h) was completely abolished, and bioactive LH values were suppressed totally. FSH, LH, testosterone and sperm counts returned to normal in all subjects following discontinuation of LHRHA infusion. Continuous infusion of 500 micrograms of LHRHA daily for 16 weeks with 100 mg of testosterone enanthate every 2 weeks induced desensitization of the pituitary, loss of LH bioactivity, and decreases of FSH and testosterone. This mode of administration, however, did not improve sperm density results obtained earlier by single daily injections of the analog. Heterogeneity of sperm density profiles still persists for reasons that are not yet clear.

Adult↗

PubMedDate not supplied

Gamma-melanotropin response to ovine corticotropin releasing factor in normal humans.

Plasma gamma-melanotropin was measured by a gamma 3MSH-specific radioimmunoassay before and after a single bolus intravenous infusion of ovine corticotropin releasing factor (oCRF; 0.1 microgram/kg) in seven normal men. A significant increase of gamma 3MSH was observed 15 minutes post-oCRF infusion, which paralleled a similar increase in plasma cortisol. Gel filtration chromatography revealed that the observed increase was attributable to elevations of 9K and 4K forms of gamma 3MSH immunoreactivity. Affinity chromatography demonstrated that the majority of gamma 3MSH immunoreactivity in human plasma is glycosylated. As the smaller forms of gamma 3MSH are felt to have endocrine activity at the adrenal cortex, these changes may be physiologically relevant.

Adult↗

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In vitro pituitary hormone releasing activity of 40 residue human pancreatic tumor growth hormone releasing factor.

The hypophysiotropic activities of a synthetic human pancreatic growth hormone releasing factor (hpGRF) with 40 residues was examined in vitro using rat pituitary halves. At concentrations from 10(-10) M to 10(-7) M the peptide stimulated GH release in a dose-dependent manner with the ED50 being 1.2 x 10(-9) M. The concentration of 10(-10) M hpGRF is comparable to the basal hypophyseal portal blood levels of other known hypothalamic hypophysiotropic hormones. However, GH release was enhanced three-fold by concentration as low as 10(-12) M, though no dose-response relationship was observed up to 10(-10) M. Thus, this peptide not only stimulates the release of GH in a dose-dependent manner, but at lower concentrations also maintains elevated GH levels. The release of ACTH, beta-endorphin, LH, and FSH was not affected by hpGRF at any of the concentrations tested. At hpGRF concentrations less than 10(-7) M, the release of TSH and PRL were unaffected. However, at 10(-6) M, TSH release was enhanced about 2.5 fold and prolactin release was elevated slightly.

Animals↗

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Effects of corticotropin releasing factor on locomotor activity in hypophysectomized rats.

Corticotropin releasing factor (CRF) injected intracerebroventricularly to hypophysectomized and sham hypophysectomized rats produced a dose dependent increase in locomotor activity, but in untreated hypophysectomized rats 10X more CRF was needed to produce a significant increase in activity. Concomitant daily supplements of rat growth hormone, thyroxine, and corticosterone to the hypophysectomized rats eliminated locomotor activity differences between the two groups. There was no statistically significant difference in locomotor response to either saline, 0.1 micrograms CRF, 1.0 micrograms CRF or 10.0 micrograms CRF in the group of animals receiving hormonal supplements. These results demonstrate that CRF can produce behavioral activation in rats independently of its effects on releasing hormones from the pituitary gland.

Animals↗

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Effect of vasoactive intestinal peptide, peptide histidine isoleucine and growth hormone-releasing factor-40 on bombesin-like immunoreactivity, somatostatin and gastrin release from the perfused rat stomach.

Bombesin-like immunoreactivity (BLI) has been demonstrated in neurons of the gastrointestinal tract and gastric BLI secretion can be demonstrated in response to the classical neurotransmitter acetylcholine. Since structurally related peptides VIP, PHI and GRF have to be considered as peptidergic neurotransmitters it was of interest to determine their effect on gastric BLI secretion. Additionally, somatostatin (SLI) and gastrin secretion was examined. The isolated stomach of overnight fasted rats was perfused with Krebs-Ringer buffer via the celiac artery and the effluent was collected via the portal vein. The gastric lumen was perfused with isotonic saline at pH7 or pH2. All four peptides were tested at a dose of 10(-11) M and 10(-8) M at both pH levels and in addition the effect of VIP and PHI was examined at 10(-14) M and 10(-12) M during luminal pH2. At luminal pH7 VIP and PHI stimulated SLI release at 10(-8) M but had no effect on BLI or gastrin secretion. rGRF and hpGRF were both ineffective on SLI and gastrin release while rGRF inhibited and hpGRF stimulated BLI secretion. This effect was not dose related. At luminal pH2 all four peptides stimulated BLI secretion. Stimulation by PHI was already observed at a dose of 10(-14) M while VIP elicited a stimulatory effect at 10(-12) M. PHI at the two lowest concentrations of 10(-14) and 10(-12) M elicited a stimulation of SLI and gastrin release while the same doses of VIP and the higher doses of all four peptides had no effect on SLI and gastrin secretion at an acidic intraluminal pH.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗

PubMedDate not supplied

Characterization of rat hypothalamic growth hormone-releasing factor.

The importance of the hypothalamus in the regulation of growth hormone (GH) secretion from the adenohypophysis has been supported by experimental and clinical evidence. It has been observed that GH secretion is in part controlled by hypothalamic GH release-inhibiting factors, two forms of which, somatostatin-14 (ref. 5) and somatostatin-28 (refs 6-9), have been characterized. Peptides with GH-releasing activity were recently purified from two human pancreatic tumours of acromegalic patients and characterized. Synthetic versions of these human pancreatic tumour GH-releasing factors (hpGRFs) were found to be potent GH secretagogues in vitro and in vivo and to exhibit actions and interactions similar to those observed with partially purified hypothalamic GRF. GH-releasing peptides have been purified from hypothalami of various species but the structure of natural hypothalamic GRF has not yet been reported. We now describe the purification, sequence analysis and synthesis of a 43-residue polypeptide isolated from rat hypothalamic extracts on the basis of its ability to stimulate GH secretion from cultured rat adenohypophyseal cells. The native polypeptide and its synthetic replicate do not differ significantly in their biological potencies and intrinsic activities. We propose that this polypeptide, which shows 67% homology with the corresponding N-terminal 43 residues in hpGRF-44, is the long-sought rat hypothalamic GRF (rhGRF).

Amino Acid Sequence↗

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Corticotropin-releasing factor is a potent inhibitor of sexual receptivity in the female rat.

Corticotropin-releasing factor (CRF), the recently characterized and synthesized 41-amino acid polypeptide isolated from ovine hypothalami, has been shown to be a potent stimulator of adenohypophyseal beta-endorphin and corticotropin (ACTH) secretion both in vitro and in vivo. In common with other regulatory peptides, CRF has also been demonstrated to possess extra-hypophysiotropic roles. Indeed, intracerebroventricularly (i.c.v.) administered CRF elicits several endocrine and behavioural responses compatible with the concept that this peptide could be a key signal in coordinating the organism's endocrine and behavioural responses to stressful and other adaptive stimuli. We now provide the first evidence for neurally placed CRF in the control of a specific hormone-dependent behavioural response and unequivocally demonstrate an extremely potent suppressive effect of CRF on sexual behaviour in the female rat when microinfused into the arcuate-ventromedial area of the hypothalamus (ARC-VMH) and the mesencephalic central grey (MCG).

Adrenocorticotropic Hormone↗

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Modulation of stress-induced ACTH release by corticotropin-releasing factor, catecholamines and vasopressin.

The stress-induced release of ACTH is believed to involve the activation of several humoral and neural pathways, including corticotropin-releasing factor (CRF), catecholamines and vasopressin. The essential role of CRF was supported by our observation that immunoneutralization of this releasing factor significantly lowers plasma ACTH levels of ether-stressed rats. However, the presence of a small but measurable residual ACTH secretion suggested the possible involvement of factors other than CRF in the stress response. We report here that pretreatment with a vasopressin antagonist decreases the plasma ACTH levels of ether-stressed rats in later (10-20 min), but not earlier (0-10 min), phases of ether stress. The ganglionic blocker chlorisondamine, inhibits ACTH release during both phases of the response to ether by 40-60% when used alone, and by 100% when administered with anti-CRF antibody. These results support a role of CRF, catecholamines and vasopressin in mediating ACTH release by ether stress.

Adrenocorticotropic Hormone↗

PubMedDate not supplied

Transcriptional regulation of growth hormone gene expression by growth hormone-releasing factor.

Production and release of hormones by the pituitary is known to be under complex hormonal control. Prolactin, for example, is both positively and negatively regulated by steroid and thyroid hormones as well as by peptide hormones. Some hypothalamic releasing factors have been shown to regulate both hormone biosynthesis and hormone release. In the case of growth hormone (GH), glucocorticoids and thyroid hormone stimulate its production, at least in part by stimulating transcription of the GH gene, and somatostatin inhibits and growth hormone-releasing factor (GRF) stimulates its release. So far, however, polypeptide hormone regulation of GH biosynthesis has not been demonstrated. Recently a peptide with GH-releasing activity has been characterized from human pancreatic islet tumours. We report here that pure human pancreatic GRF (hpGRF) stimulates transcription of the GH gene, as well as stimulating GH release.

Animals↗

PubMedDate not supplied

Expression-cloning and sequence of a cDNA encoding human growth hormone-releasing factor.

Growth hormone-releasing factor (GRF) is believed to mediate both neural and hormonal control of the release and perhaps synthesis of growth hormone (GH) from the anterior pituitary. Its presence in only minute quantities in the hypothalamus hampered for many years efforts to determine its structure. Recently, two groups independently characterized a peptide from two human pancreatic tumours that possessed GH-releasing activity. Antibodies to this peptide have revealed immunoreactive material in the hypothalamus of several primate species. Furthermore, an apparently identical peptide has now been isolated directly from human hypothalamus. Using both oligonucleotide and antibody screening of a cDNA expression library, we have isolated a recombinant clone encoding human pancreatic GRF (hpGRF) within a larger precursor protein. The nucleotide sequence predicts that processing of GRF from the precursor should generate two additional peptides of unknown function. Restriction analysis of genomic DNA indicates that there is probably a single human GRF gene and suggests that the pancreatic tumour and hypothalamic proteins are encoded by an identical mRNA.

Amino Acid Sequence↗

PubMedDate not supplied

Binding sites for growth hormone releasing factor on rat anterior pituitary cells.

Growth hormone releasing factors (GRFs) have been isolated from human pancreatic tumours (hGRF) and rat hypothalamus (rhGRF). The response to GRF at the pituitary level can be modulated by other factors, including glucocorticoids, thyroid hormones, somatostatin and other neuropeptides and somatomedins. Glucocorticoids enhance GRF-induced growth hormone (GH) secretion in primary cultures of rat anterior pituitary cells, and the synthetic glucocorticoid dexamethasone has recently been shown to increase the amounts of GH released in freely moving rats in response to submaximal doses of intravenous GRF. To investigate whether somatotroph sensitivity to GRF is modulated at its receptor level, we have developed a radioreceptor assay using an iodinated analogue of hGRF as radioligand. We report here that the relative binding affinities of rGRF, hGRF and the two analogues are correlated with their in vitro biological potencies. Further, the number of GRF binding sites is drastically decreased in cells deprived of glucocorticoids either in vivo or in vitro.

Adrenalectomy↗