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The early effects of pinealectomy on LH and testosterone secretion were studied in 11 white-tailed bucks. Six bucks were pinealectomized and three were sham-operated in early March at 9 months of age. Two unoperated bucks of the same age were also followed. The response of the pituitary gland and testis to LH releasing hormone (LHRH) was monitored for 2 h each month for 1 year by radioimmunoassay of serum LH and testosterone. Prestimulation levels of LH (expressed as µg NIH-oLH-S7) exhibited a cosinor curve pattern over the year (P < 0·002) with levels ranging between 0·1 and 3·9 µg/l. Highest levels in pinealectomized males occurred in May 2 months after surgery and in control (sham-operated and unoperated) males in August. Maximal LH response to LHRH was characterized by a double-peaked curve in serum LH with the early peak around 20 min and a later peak at about 2 h after injection. Maximal response to LHRH occurred in May in pinealectomized bucks and in August in control bucks. Baseline testosterone concentrations and testosterone response to LHRH varied in a seasonal fashion throughout the 12-month period in control bucks (P < 0·001 ) but not in pinealectomized bucks. Baseline testosterone concentration and testosterone response to LHRH rose within 2 months after surgery in pinealectomized bucks and remained relatively constant for the next 10 months. These data demonstrate an early effect of pinealectomy on LH and testosterone secretion in 9-month-old animals kept under conditions of natural photoperiod and suggest differences in the response to pinealectomy by the pituitary gland and testes. Furthermore, the effect appears to be a release from suppression early after pinealectomy followed by a disruption of the normal sequence of events related to the autumn rut.

J. Endocr. (1984) 103, 1–7