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Immunoreactive endothelin-1 (IR-ET-1) was detected in the cultured medium from endometrial but not myometrial cells of rabbits in primary culture using a specific radioimmuno assay (RIA). Similar results were obtained with a radioreceptor assay using myometrial membranes. In a reverse-phase HPLC synthetic ET-1 and IR-ET-1 of the extract medium from endometrial cells revealed essentially the same elution profiles, as determined by RIA. Two selective agonists of oxytocin (OT) or V1 vasopressin (VP) receptors produced, respectively, a 6- and 2-fold increase of IR-ET-1 release from endometrial cells. These effects were completely reversed by the addition of two specific antagonists of OT and V1 VP receptors. Our results indicate that ET-1 is produced and released in the culture medium of rabbit endometrial cells in primary culture. The release of ET-1 is under receptor-specific control by neurohypophyseal hormones.

In attempting to elucidate the neuroendocrine mechanisms that regulate pulsatile growth hormone (GH) secretion, we measured serum GH concentrations by an ultrasensitive immunofluorometric method in blood collected every 10 min for 8 h in 11 young healthy male volunteers (age range 21-31 yr) before and during somatostatin (SS) administration (an iv bolus dose of 350 micrograms followed by a continuous infusion at the rate of 6 micrograms.kg-1.h-1, which increases the circulating SS levels to approximately 570 pg/ml). Pulsatile GH secretion was analyzed using the computer-assisted pulse detection program cluster method and deconvolution analysis. The area and frequency of GH peaks were significantly reduced during SS infusion compared with basal values, but detectable pulsatile episodes were still present. These data suggest that, in adult males, SS controls pulsatile GH secretion and can decrease the mass and frequency of GH secretory bursts.

SUMMARY A radioimmunoassay for the determination of testosterone in human plasma is described. After extraction from plasma, testosterone is separated by paper chromatography. The radioimmunoassay is performed using an antiserum to testosterone‐3‐oxime‐rabbit serum albumin and a saturated solution of ammonium sulphate is used for separation. The reliability criteria of the method in terms of precision, accuracy, sensitivity and specificity have been evaluated. The mean level of testosterone in plasma samples from nineteen normal men (age range 16–73 years) is 527±226 (±SD) ng/100 ml. In ten normal ambulatory females (in the second phase of the cycle) aged 19–35 years the mean plasma testosterone is 27±8±10±6 (±SD) ng/100 ml. In twenty‐four impotent men (aged 18–50) the testosterone level is 431±191 (mean±SD) ng/100 ml. These values are not significantly different from normal subjects. Lastly, the testosterone levels found in a few cases of male hypogonadism are reported.

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