The Profile of LH and Testosterone Secretion in the Ram

Abstract

The secretory pattern of luteinizing hormone (LH) and testosterone (T) and the temporal relationship between the two were studied in 4 mature rams (2–3 yr of age). Blood was obtained from the jugular by venipuncture at 20-min intervals for a 24 hr period from each of 2 crossbred rams in May and 2 Finnish Landrace rams in August and January. Serum levels of LH and T were determined in duplicate by RIA. LH estimations have been expressed in terms of ng NIH-LH-S14/ml. Rams sampled in May and August exhibited similar LH and T secretory patterns. Baseline levels of LH fluctuated from 0.20–0.94 ng/ml. During the 24-hr period each ram exhibited from 3–5 LH peaks averaging 9.59 ± 1.50 ng/ml and occurring at intervals of 6.9 ± 0.6 hr. Within 1 hr following each LH peak the blood T level consistently increased from baseline values of 0.30–1.53 ng/ml to peak values averaging 9.02 ± 1.53 ng/ml. The secretory pattern in January for the 2 Finnish Landrace rams differed considerably from that in August. For each ram 7 LH peaks were observed during the 24 hr, averaging 1.80 ± 0.55 ng/ml and occurring at intervals of 3.9 ±0.1 hr. LH releases were followed by increases in T which peaked at 19.66 ± 0.42 ng/ml within 40 min. We concluded that LH releases were occurring at random among the rams as elevations did not consistently occur at any particular hour. For each ram however, LH releases occurred at regular intervals and were always followed by sudden, dramatic increases in blood T. Under conditions of this study no consistent relationship was found to exist between the magnitude of the LH and resultant T peaks. (Endocrinology95: 627, 1974).