Pituitary and gonadal response to exogenous LH-releasing hormone in the male domestic cat.

To determine the influence of exogenous LH-releasing hormone (LHRH) on serum LH and testosterone, ten adult male domestic cats received three treatments on a rotating schedule at 10-day intervals as follows: (I) 0.1 ml saline i.m. (control); (II) 10 micrograms LHRH i.m., single injection; (III) 10 micrograms LHRH i.m., two injections given at a 2-h interval. Serial blood samples collected over a 360-min interval were analysed by radio-immunoassay for LH and testosterone. Although baseline serum LH values in saline-treated animals (treatment I) varied markedly among individual cats (2.2-29.2 micrograms/l), there was no evidence of pulsatile LH release or alterations in testosterone over time within individual males. In treatment II, the single injection of LHRH induced a rapid rise in mean serum LH within 30 min in all cats (mean peak, 88.2 +/- 9.8 micrograms/l), which returned to baseline by 120 min after LHRH. Mean testosterone increased within 30 min in this group (from 6.03 +/- 2.18 to 18.55 +/- 3.36 nmol/l), peaked at the 60-min collection (19.76 +/- 2.77 nmol/l) and returned to baseline by the 150-min sample. After treatment III, serum LH peaked at 131.6 +/- 13.6 micrograms/l within 30 min of the initial LHRH injection. A second injection of LHRH produced another LH surge within 30 min, but in all cats this second response was of a lower magnitude (mean peak, 69.0 +/- 14.5 micrograms/l) and shorter duration (P less than 0.05). The second LHRH injection sustained peripheral testosterone levels for approximately 1 additional h.(ABSTRACT TRUNCATED AT 250 WORDS)