Metabolism of exogenous human chorionic gonadotrophin in men

The immunoreactivity of a commercial preparation of human chorionic gonadotrophin (HCG) was determined in a homologous double antibody radioimmunoassay for HCG using antisera to the beta-subunit of the hormone. The immunoreactivity of the commercial HCG was found to be 2.2 +/- 0.3 (mean +/- 2 S.D.) times the biological potency. Exclusion chromatography of the commercial HCG and then curve resolution of the elution profile derived from the radioimmunoassay revealed that on a molar basis, 21% of the immunoreactivity was attributable to beta-HCG. The rate of clearance of this preparation of HCG from the plasma after intravenous administration was determined as a function of the dose administered to ten normal men (age 36--64 years). The doses ranged from 10,000 to 300,000 i.u. immunological potency. The rate of clearance decreased significantly (r = 0.574, P less than 0.05) with increasing doses of HCG from a mean of 786 ml/h at the lowest dose to a mean of 298 ml/h at the highest dose. The renal clearance of administered HCG also decreased with increasing doses; the mean renal clearance of the 10,000 i.u. dose was 3.6 times the mean renal clearance after administration of 200,000 i.u. When the accumulated urinary HCG was expressed as a percentage of the dose administered, 14.1% of the 10,000 i.u. dose and 9.8% of the higher doses accumulated in the urine, suggesting that non-renal clearance increased with increasing dose.

Hyperprolactinaemia in the spontaneously hypertensive rat

A hypothalamic role in the aetiology of hypertension in the spontaneously hypertensive rat (SHR) has been suggested by prior observations. In an attempt to determine whether the central control of prolactin (PRL) release is altered in the SHR we have compared the PRL response to immobilization stress, thyrotrophin releasing hormone (TRH), haloperidol, and L-DOPA in the SHR and in normotensive Wistar control rats. Carotid artery catheters were inserted 48 h prior to the PRL response studies and the catheters were maintained patent with heparinized saline. Timed blood samples were obtained in SHR and control rats weighing 180-225 g. The SHR demonstrated elevated basal serum levels of PRL and greater PRL responses to stress. However, administration of L-DOPA resulted in a similar suppression of serum PRL in the SHR and in the normotensive controls. These findings suggest alteration in the central control of PRL release in the SHR. Observations of elevated basal PRL, exaggerated PRL in response to L-DOPA in SHR are consistent with normal pituitary responsiveness to dopamine suppression of PRL release, but defective hypothalamic metabolism of dopamine. Alterations in central dopamine control mechanisms in the SHR may play a role in the pathogenesis of essential hypertension in these animals.

Pituitary response to LHRH in midtrimester pregnancy

The effects of lutenizing hormone releasing hormone (LHRH) on serum luteinizing hormone (LH), follicle stimulating hormone (FSH), prolactin (PRL), thyroid stimulating hormone (TSH), and growth hormone (GH) were studied in 10 women in the second trimester of pregnancy. Serum LH was measured using the LHbeta-RIA, with the anti-betaLH serum being preabsorbed with purified hCG. This assay was unaffected by hCG levels up to 500 IU/ml. Basal serum levels of LH was undetectable and basal FSH levels were low in these 10 women. No release of LH or FSH was observed after administration of 100 microgram of LHRH. However, there was a statistically significant rise in PRL from mean basal levels of 139.9 ng/ml to a mean peak level of 159.0 ng/ml at 30 minutes after LHRH administration. Both TSH and GH displayed small elevations at 15 minutes after LHRH administration; however, these elevations were not significant because of the wide range in responses. The results of this study indicate that gonadotropin release is inhibited during the second trimester of pregnancy. Finally, it appears that pregnancy is a condition in which LHRH administration results in a nonspecific release of several hormones.

The effect of intra-amniotic prostaglandin F2alpha on anterior pituitary hormone release during midtrimester abortion

The effect of intra-amniotic administration of prostaglandin F2alpha (PGF2alpha) on pituitary hormone release was studied in women undergoing midtrimester abortion. Serum prolactin (PRL), growth hormone (GH), thyrotropin (TSH), luteinizing hormone (LH), and follicle-stimulating hormone (FSH) were measured prior to and at 15-minute intervals for 2 hours following intra-amniotic administration of 40 gm of urea alone, 20 mg of PGF2alpha and 40 gm of urea, or an equal volume of normal saline. Serum PRL levels were significantly higher at sampling times from 15 through 120 minutes when both PGF2alpha and urea were administered than after saline or urea alone. The elevation in serum GH following PGF2alpha and urea was not significantly greater than for urea alone. The GH response in the women receiving normal saline was significantly less than for the two groups of women receiving the abortifacients. These results indicate that the GH response was related to the stress effects of the abortifacients. There was no difference in the TSH, LH, and FSH responses for the three groups. These results suggest that PGF2alpha selectively causes pituitary release of PRL in women during midtrimester pregnancy.

Effect of human chorionic gonadotropin on thyroid function in euthyroid men

The effect of large doses of commercial hCG on thyroid function was studied in eight men who received 100,000 or 150,000 IU hCG iv. These large doses of hCG produced definite thyroidal iodine release (TIR) responses in all eight men. The TIR after hCG administration was more delayed and of lesser magnitude than the TIR responses to TSH and TRH. There were no significant changes in serum T4, T3, or TSH for 48 h after hCG administration. No clinical side effects were noted in the subjects after iv administration of these large doses of hCG. The results of this study indicate that hCG is a weak thyroid stimulator in man.

The use of intramuscularly administered methyl-TRH to evaluate the pituitary-thyroid axis

The present study was carried out to evaluate the effectiveness of intramuscular administration of methyl-TRH, a potent analogue of thyrotropin-releasing hormone, for assessing pituitary reserve of TSH and prolactin and for distinguishing euthyroid, hypothyroid and hyperthyroid individuals. Serum samples were taken for 24 hours after intramuscular injection of methyl-TRH, 200 microgram, in 19 euthyroid subjects, 9 hypothyroid men and 9 hyperthyroid men. The mean serum prolactin and TSH concentrations were significantly elevated over baseline levels at 30 min in the euthyroid individuals and remained elevated for 3 to 4 hours. The serum TSH, T3 and T4 responses after intramuscular methyl-TRH in euthyroid subjects were clearly distinguishable from those of hyperthyroid and hypothyroid patients. Significant elevation of the serum T3 and T4 concentrations at 24 hours after intramuscular injection of methyl-TRH shows the sustained effect of this TRH analogue in euthyroid subjects.

Influence of methyl-TRH-induced prolactin increase on serum testosterone levels in normal adult men

Our previous studies suggest that increased serum PRL, secondary to haloperidol-induced dopamine blockade, augments serum testosterone (T) levels in normal men. To rule out a direct effect of haloperidol on the testis, serum samples from a methyl-TRH study in normal men, in whom serum PRL levels were increased by a stimulus other than dopamine blockade, were analyzed for T. Fourteen subjects received both a low dose (6.25-12.5 micrograms) and a high dose (100-500 micrograms) of methyl-TRH on separate days; blood sampling was done for 15 min before and for 4 h after drug infusion. Compared to a saline control group of 14 normal men, who showed a diurnal decline of serum T levels, the methyl-TRH treated subjects had statistically significant increases in serum T after both low and high doses. These data provide further support for the concept that PRL is a pituitary hormone capable of augmenting serum T levels in normal adult men.

The effect of stressful diagnostic studies and surgery on anterior pituitary hormone release in man

The hormonal response of the anterior pituitary was studied in 10 normal males undergoing treadmill exercise testing, in 5 male patients undergoing diagnostic gastroscopy, and in 8 male patients undergoing elective surgery under general anaesthesia. Serum TSH was depressed below the baseline value at 2 and 3 h post-treadmill exercise, at 1, 2 and 3 h post-gastroscopy and from 10 min through 2 h post-surgery. Serum triiodothyronine was depressed below the baseline value at 10 min through 2 h post-surgery. Serum prolactin, growth hormone and cortisol were elevated by all three stressful procedures. Both gastroscopy and surgery resulted in an elevation of serum luteinizing hormone levels. There was no significant change in serum FSH levels in any of the three procedures. The post-stress depression in TSH levels could result from the suppressive effect at the hypothalamic-pituitary level of high serum levels of cortisol generated by the stress of the procedures.

Lack of effect of thyroid hormones on the growth hormone response to thyrotropin-releasing hormone in acromegaly

Serum growth hormone (GH) responses to thyrotropin-releasing hormone (TRH) were evaluated in 14 patients with acromegaly following treatment with thyroid hormones. After an initial TRH test, seven patients received L-triiodothyronine, 100 mug daily for seven days; the GH response to TRH was not significantly altered by this treatment. Similar findings were noted in two acromegalic subjects who were tested with TRH before and after longer periods of administration of L-thyroxine. Four of five additional subjects with acromegaly who had received replacement doses of thyroid hormones for an average of 6.6 yr demonstrated GH responses to TRH which were similar to those seen in subjects not receiving thyroid hormones. Acute or long-term administration of replacement doses of thyroid hormones seems to have minimal effect on the GH response to TRH in acromegaly.

Osmotic control of the release of prolactin and thyrotropin in euthyroid subjects and patients with pituitary tumors

The effects of acute changes in serum osmolality on basal serum PRL and TSH levels and on responses of prolactin (PRL) and thyrotropin (TSH) to the thyrotropin-releasing hormone (TRH) analogue, N3im-methyl-TRH, were studied in ten euthyroid subjects and in three patients with PRL-secreting pituitary tumors. An oral water load of 20 ml/kg had no effect on basal serum PRL or TSH levels but did result in an increased PRL response to methyl-TRH in the ten euthyroid patients. Intravenous infusion of 5% sodium chloride in the ten euthyroid subjects significantly depressed basal serum PRL levels but had no effect on the PRL response to methyl-TRH. Infusion of hypertonic saline significantly decreased the TSH response to methyl-TRH. In the three patients with pituitary tumors, oral water loading and hypertonic saline infusion had no significant effect on the basal serum PRL and TSH or the PRL and TSH responses to methyl-TRH. The patients with pituitary tumors had a higher basal serum osmolality and a proportionately higher serum concentration of arginine vasopressin than the euthyroid patients. These data suggest that changes in osmolality in euthyroid patients may have a direct effect on the anterior pituitary's PRL and TSH response to a releasing factor.

Effect of dexamethasone on prolactin and TSH responses to TRH and metoclopramide in man

We studied the effects of administration of dexamethasone, 2 mg orally every 6 h, for 5 days on the thyrotropin-releasing hormone (TRH)-induced release of prolactin (PRL), thyrotropin (TSH), triiodothyronine (T3) and thyroxine (T4) in 9 normal men and on the metoclopramide-induced release of PRL in 7 normal men. Dexamethasone suppressed the baseline serum levels of PRL, TSH and T3. The administration of dexamethasone blunted the PRL and TSH response to TRH; the blunted TSH response resulted in a decreased T3 and T4 response to TRH after dexamethasone. Following dexamethasone administration, the PRL response to metoclopramide, a dopamine antagonist which acts at the hypothalamicpituitary level to stimulate PRL secretion, was blunted in 7 normal men. The data suggest that short-term administration of pharmacological doses of glucocorticoids suppress the secretion of PRL and TSH by a direct effect on the anterior pituitary gland.

Prolactin response to N3im-methyl-thyrotropin releasing hormone in euthyroid subjects

The N3im-methyl analogue of thyrotropin releasing hormone (methyl-TRH) was compared with ordinary TRH as a prolactin (PRL) releaser in 32 euthyroid volunteers (20 male and 12 female, ages 17-66 years). The mean PRL response to 100 mug of methyl-TRH was greater (P less than 0.025) than the PRL response to 500 mug of TRH at 10 min and at all sampling times from 30 to 240 min after administration of the releasing factors. The mean peak PRL (at 10 min), maximum deltaPRL, and integrated PRL response area were greater (P less than 0.025) after administration of methyl-TRH than after TRH. The PRL response to methyl-TRH was greater (P less than 0.005) for the 12 women than for the 20 men in this study. The mean baseline PRL was correlated with the peak PRL (r=0.74, P less than 0.01) and the maximum deltaPRL (r=0.58, P less than 0.01) after methyl-TRH. Following administration of methyl-TRH, the peak PRL was correlated with the peak TSH (r=0.43, P less than 0.05), the maximum deltaPRL was correlated with the maximum deltaTSH (r=0.43, P less than 0.05), and integrated PRL response area was correlated with the integrated TSH response area (r=0.44, P less than 0.05). Similar correlations between PRL and TSH responses were seen after giving TRH. Age was inversely correlated with baseline PRL (r=-0.55, P less than 0.01), with maximum deltaPRL (r=-0.64, P less than 0.01), and with the PRL response area (r=0.48, P less than 0.01) after administration of methyl-TRH or TRH. Methyl-TRH did not significantly alter serum levels of growth hormone (16 subjects) and luteinizing hormone and follicle stimulating hormone (14 subjects). The results of this study indicate that methyl-TRH is a more potent prolactin releaser than TRH. Like TRH, methyl-TRH has specificity in its effects on the pituitary, releasing only TSH and PRL in normal man.

Dose-response of prolactin and thyrotropin to N3im-methyl-thyrotropin releasing hormone in euthyroid men

The synthetic N3im-methyl analogue of thyrotropin releasing hormone (methyl-TRH) was administered intravenously to 15 euthyroid men, ages 36-62, in graded doses from 6.25 mug to 500 mug in order to establish the range of response of prolactin (PRL), TSH, T3 and T4 to various doses of methyl-TRH. There was a dose-related rise in serum TSH, PRL, T3, and T4 which gave a nearly linear relationship when the integrated area of response was used as an index of response to the various doses of methyl-TRH. All 15 men had a clear elevation in TSH, PRL, T3 and T4 following the lowest dose of methyl-TRH TESTED (6.25 mug). There was considerable variability in the response to methyl-TRH among the individuals. One hundred mug of methyl-TRH gave a maximum TSH response; a 25 mug dose elicited a maximum PRL response.

Effect of N3im-methyl-thyrotropin releasing hormone on the human pituitary-thyroid axis

The N3im-methyl analogue of thyrotropin release hormone (methyl-TRH) was compared with TRH as a thyrotropin releaser in 30 euthyroid volunteers (ages 19-61 years). The mean TSH response to 100 mug of methyl-TRH was greater (P less than 0.005) than the TSH response to 500 mug of TRH from 10 min to 240 min after giving the releasing factors. The mean peak TSH (at 30 min), maximum deltaTSH, and integrated TSH response area were greater (P less than 0.005) after administration of methyl-TRH than after TRH. The TSH response to methyl-TRH was significantly greater (P less than 0.05) for the 11 females than for the 19 males in this study. The mean baseline TSH was correlated with the maximum deltaTSH (r = 0.72, P less than 0.01) after methyl-TRH stimulation. The mean serum T3 concentration after methyl-TRH was significantly elevated at 60 min, peaked at 210 min and remained significantly elevated at 240 min. The peak serum T3, maximum T3 and T3 response area were significantly greater (P less than 0.005) after giving methyl-TRH than after TRH. The methyl-TRH induced T3 response area was 1.4 times the TRH induced T3 response area. The serum T4 concentration after methyl-TRH was elevated at 90 min (P less than 0.005), reached a peak at 210 min, and at 240 min was still 1.25 times the mean baseline T4. The peak serum T4, maximum deltaT4 and T4 response area after methyl-TRH were significantly greater than after TRH. The methyl-TRH induced T4 response area was 1.4 times the TRH induced T4 response area. The data indicate that methyl-TRH is a more potent thyrotropin releaser than TRH. Since N3im-methyl-histidine has been found in the brain, the possibility that this methyl analogue of TRH is a physiologic thyrotropin releaser should be evaluated.

Comparison of metoclopramide with other dynamic tests of prolactin secretion

Metoclopramide, a derivative of procainamide, was compared with thyrotropin releasing hormone (TRH), N3im-methyl-TRH and chlorpromazine as a prolactin (PRL) releaser in 11 euthyroid males. The peak response of serum PRL and the maximum increment of serum PRL (max deltaPRL) were greater (P less than 0.0005) after the administration of metoclopramide (deltaPRL 24.1 +/- 1.5 (SE) ng/ml) than after either TRH (14.9 +/- 1.5 ng/ml) or chlorpromazine (7.0 +/- 2.1 ng/ml). There were no significant differences between the peak and max deltaPRL responses to metoclopramide or N3im-methyl-TRH. Metoclopramide produced a small increase in serum thyrotropin and small reductions of serum growth hormone, luteinizing hormone and follicle-stimulating hormone. Metoclopramide may be useful for dynamic testing of PRL release. It offers the advantage of oral administration; a 10 mg dose produces a larger, more sustained increment in serum PRL than other agents used to evaluate prolactin reserve.

Metoclopramide stimulates prolactin secretion in man

Serum prolactin concentrations increased approximately 6-fold after oral or intravenous administration of 10 mg of metoclopramide to adult men. Prolactin remained significantly elevated up to 9 h after oral metoclopramide and for at least 2 h after iv metoclopramide. Bethanechol did not increase serum prolactin, and atropine did not inhibit metoclopramide-induced prolactin elevation, suggesting that the cholinergic-like properties of metoclopramide were not responsible for the observed prolactin responses. Pre-treatment with 500 mg L-dopa inhibited the early metoclopramide-induced prolactin increase, which is consistent with the possibility that metoclopramide acts by inhibiting dopamine-mediated hypothalamic secretion of prolactin inhibitory factor. As a potent stimulus of prolactin release, metoclopramide may be useful in clinical investigation of hypothalamic-pituitary function.

Effect of TRH on serum arginine vasopressin in euthyroid and hypothyroid subjects

To test the effect of thyrotropin-releasing hormone (TRH) on serum arginine vasopressin (AVP) in euthyroid and hypothyroid individuals, 500 mug of TRH was administered to four euthyroid subjects and three patients with primary hypothyroidism. Serum AVP was significantly depressed below basal levels from 30 to 60 min in the euthyroid and hypothyroid subjects after administering the releasing agent. The basal serum AVP in the hypothyroid subjects (3.1 +/- 1.1 muU/ml) was not significantly greater than the basal serum AVP in the euthyroid subjects (2.8 +/- 1.2 muU/ml). The maximal incremental depression in serum AVP after TRH in the hypothyroid subjects (1.4 +/- 0.7 muU/ml) was similar to the depression observed in the euthyroid subjects (1.8 +/- 0.9 muU/ml). These data suggest that TRH may have a physiologic role in modulation of AVP release in man.