Plasma luteinizing hormone and testosterone in the adult male pig: 24 hour fluctuations and the effect of copulation.

Secretory patterns of LH and testosterone were characterized in the intact male miniature pig. All blood samples were taken from indwelling catheters. Hourly sampling was carried out over 24 h and during a morning period blood was collected for 2 h at 10 min intervals. No significant difference was detected in the plasma LH concentration on the basis of hourly sampling. Plasma testosterone was significantly (P less than 0-05) lower during the evening and night when compared with morning values. The second experiment was concerned with the pattern of plasma LH and testosterone concentrations before and after copulation. Blood sampling was performed at 10 min intervals. Plasma LH was significantly (P less than 0-001) raised for 30 min after copulation when compared with any 30 min period (0-120 min) before copulation. Plasma testosterone was not significantly altered for any 30 min period of the experiment (0-270 min). The data are interpreted as a possible mechanism for endocrine control of testicular function.