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. (Endocrinology 95: 627, 1974).A PULSATILE secretion of luteinizing horjt\. mone (LH) and testosterone (T) has been observed in the male of a number of species. Assay of frequently collected serial blood samples from the human has revealed that both LH (1,2) and T (3,4,5) are secreted in spurts but there is no apparent cause and effect relationship between these two hormones. A pulsatile secretory pattern also exists for LH and T in the bull (6,7) and ram (8,9,10,11). Although LH releases are usually followed by increases of blood T levels in the bull, evidence to date suggests that this relationship does not occur in the ram (10,11).Results of previous studies involving determination of serum LH and T fluctuations in the ram have been obtained from hourly or less frequent blood samplings. However, the halflife of LH in the peripheral blood of sheep has been determined to be approximately 30 min (12). Therefore, in order to more accurately de-R3T 2N2.termine the secretory pattern of and the temporal relationship between LH and T in the ram we sampled 4 mature rams at 20-min intervals for 24-hr periods. Results indicate that a definite relationship exists between LH releases and sudden, dramatic increases in serum T and, add further support to the suggestion (9) that the secretory pattern for LH and T is altered from season to season in the ram.

Seasonal variation in LH and testosterone release in rams of two breeds

“…(Lincoln, 1979 (Terqui et al, 1980). Findings of an apparent absence of relationship between LH and testosterone levels in rams may only be the result of too infrequent sampling (Falvo et al, 1975 The present results confirm that the numbers of LH and testosterone peaks increase from the non-breeding to the breeding season (Sanford et al, 1974(Sanford et al, , 1977Schanbacher & Ford, 1976;Wilson & Lapwood, 1978 …”

“…There is general agreement that the number of LH and testosterone peaks increases when animals pass from the non-breeding season to the breeding season (Sanford et al, 1974(Sanford et al, , 1977Schanbacher & Ford, 1976;Wilson & Lapwood, 1978). However, the influence of genotype on the magnitude of this increase in pulsatility has until now been neglected although it may be of importance because the mean plasma testosterone concentration varies in rams of different breeds (Schanbacher & Lunstra, 1976; Gamier, Cotta & Terqui, 1978).…”

Influence of Sexual Activity on Serum Levels of Lh and Testosterone in the Ram

“…The observations in Fig. 2 have been reported previously by Sanford et al (1974) Sanford et al 1974).…”

Seasonal pattern of LH and testosterone secretion in adult male fallow deer, Dama dama

“…This relationship has been well documented for other seasonally breeding ruminants such as sheep (Katongole et al, 1974;Sanford et al, 1974;Lincoln, 1976;Schanbacher & Ford, 1976;Wilson & Lapwood, 1978) but has received little scrutiny in deer, mainly due to difficulties associated with handling these animals.…”