The Effects of Active Immunization with Testosterone on Pituitary-Gonadal Feedback in the Male Rhesus Monkey (Macaca mulatta)

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Abstract
Previous studies on the biological effects of active immunization with steroids have concentrated mainly on events occurring at one point in time only. Characteristically, increased testicular and pituitary activity were found. To investigate whether this situation can be maintained for prolonged periods, we have studied 4 adult male rhesus monkeys for 1 year after active immunization with testosterone (T). Eight normal monkeys served as control animals. Serum T, dihydrotestosterone (DHT) and LH were measured, also the antibody titer and the percentage binding of T in serum collected at weekly intervals. T levels increased as antibody titers appeared and reached concentrations 60–200-fold of normal values. A sharp peak occurred in LH after 7–9 weeks, but concentrations returned to basal levels and below after 25 weeks of immunization. T levels remained elevated in the presence of falling LH concentrations. Changes in DHT paralleled those of T. Events following immunization with T showed a biphasic response. During the first 5 months, increased testicular T production was accompanied by periods of increased LH secretion. During the later phases, circulating T levels remained grossly elevated in the presence of low or normal LH levels. It is postulated that some factor other than LH is acting on the Leydig cells, maintaining the increased T production.

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