Effects of gonadectomy and oestradiol treatment on plasma luteinizing hormone concentrations in the marmoset monkey, Callithrix jacchus.

A heterologous double-antibody radioimmunoassay for marmoset LH is described in detail. The system uses NIAMDD rat LH-I-1 for iodination, NIAMDD rat LH-RP-1 as standard and anti-ovine rabbit LH 610V serum. The assay measures the level of marmoset LH in plasma and shows a maximum cross-reaction (B/Bo = 50%) of 0.3% with other rat, human or bovine pituitary hormones. The heterologous assay has been applied to the measurement of the level of LH in the marmoset after gonadectomy and after the subsequent implantation of oestradiol-17beta capsules. A clear increase in the concentration of LH in the plasma was observed by day 3 after gonadectomy and in most animals the level reached a plateau by day 9. The rates of increase in the concentration of LH and the maximum levels attained after gonadectomy were similar in male and female marmosets. The secretion of LH in long-term gonadectomized marmosets was episodic. In four of the marmosets studied, the frequency of the pulsatile discharges of LH was circhoral, whereas in the remaining five animals the frequency could not be determined. Subcutaneous implants containing oestradiol-17beta were seen to have a biphasic effect on the secretion of LH in all gonadectomized marmosets. After a transient increase in the concentration of LH (positive feedback) on day 1, levels fell markedly by day 4 and were undetectable 8 days after the implants were introduced (negative feedback).