Opioid-receptor blockade blunts growth hormone (GH) secretion induced by GH-releasing hormone in the human male

OBJECTIVE

To investigate the existence of an opioid stimulatory tone on growth hormone (GH) secretion in the human male.

DESIGN

Seven healthy male volunteers, aged 19-30, were studied in the Endocrine Unit of the University of Sassari. GH-releasing hormone (GHRH), 100 micrograms as an intravenous (IV) bolus, as administered with and without preadministration of IV naloxone, 2 mg as a bolus followed by a constant infusion of 2 mg/h. Blood samples were taken for 120 minutes after GHRH administration.

RESULTS

Naloxone significantly blunted the GH response to GHRH, measured either as mean peak value (at times 30 to 90) or as integrated concentrations.

CONCLUSIONS

Naloxone is able to decrease the effect of a maximal dose of GHRH, thus suggesting the existence of an opioid stimulatory tone on GH secretion.

Pulsatile gonadotrophin secretion in hypothyroid women of reproductive age

Hypothyroid women may have various disturbances of the reproductive system. Although menstrual cycle disturbances and infertility have been reported in hypothyroidism, gonadotrophin levels have usually been found in the normal range. We have investigated whether female hypothyroid patients of reproductive age have any alteration in the pulsatile secretory pattern of gonadotrophin secretion. LH and FSH were assayed on days 2-5 of the menstrual cycle in blood samples taken every 10 min for 8 h from six hypothyroid women and six age-matched control subjects. Pulsatility was analysed using the Cluster and Detect programs. There was no significant difference in the number of peaks identified (3.7 +/- 0.8 vs 3.7 +/- 0.8 for LH, and 3.7 +/- 0.8 vs 4.2 +/- 0.5 for ESH), the mean duration of peaks (LH: 68.0 +/- 6.9 vs 72.7 +/- 5.1 min; FSH: 81.9 +/- 8.1 vs 71.2 +/- 10.3 min), the area under the peaks (LH: 91.5 +/- 20.4 vs 148.2 +/- 55.1 IU/l per min; FSH: 71.5 +/- 4.5 vs 62.7 +/- 15.0 IU/l per min), and the incremental amplitude from baseline (LH: 2.2 +/- 0.4 vs 3.0 +/- 0.8 IU/l; FSH: 1.4 +/- 0.2 vs 2.1 +/- 0.5 IU/ l). However, the absolute pulse amplitude was greater in hypothyroid patients (LH: 14.5 +/- 1.4 vs 8.3 +/- 1.3 IU/l, P < 0.01; FSH: 9.0 +/- 1.5 vs 5.8 +/- 1.2 IU/l, P = 0.04), as were the integrated concentrations (LH: 6.6 +/- 0.7 vs 3.2 +/- 0.4 IU/l per min, P < 0.01; FSH: 4.3 +/- 0.4 vs 2.1 +/- 0.5 IU/l per min, P < 0.01). Oestradiol values were comparable in the two groups (42.7 +/- 0.4 vs 43.5 +/- 9.7 pg/ml). These results indicate that in hypothyroid women there is an increased baseline level with a normal pulsatility of the gonadotrophin secretion. Similar oestrogen levels in both groups, and normal or near-normal cycles in our patients suggest either a decreased biological potency of the gonadotrophins or a mild ovarian resistance.