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.

Summary. Jugular vein blood was collected daily from four mature ewes throughout anoestrus and the first oestrous cycle of the breeding season until 4 days after the second oestrus. The levels of oestrogen, progesterone and LH were determined by radioimmunoassay. There were fluctuations in the LH level throughout most of the observed anoestrous period with a mean \ m=+-\ S.E. value of 2\m=.\3\ m=+-\ 0\m=.\9 ng/ml. High LH values of 20\m=.\0, 41\m=.\2and 137\m=.\5 ng/ml were observed in three ewes on Day \m=-\24of anoestrus. A brief minor rise in progesterone level was also observed around this period. Progesterone levels were consistently low (0\m=.\11 \ m=+-\ 0 \ m= . \ 0 1 ng/ml) before Day \m=-\25of anoestrus. A major rise occurred on Day \m=-\12 of anoestrus and this was followed by patterns similar to those that have been previously reported for the oestrous cycle of the ewe. Random fluctuations of oestrogens deviating from a mean level of 4\m=.\40 \ m=+-\ 0\m=.\1 pg/ml were observed during anoestrus and the mean level during the period from the first to the second oestrus was 5\m=.\2\ m=+-\ 0\m=.\3 pg/ml. A wel l \x=req-\ defined peak of 13\m=.\3\ m=+-\ 0\m=.\7 pg/ml was seen in all ewes on the day of the second oestrus. Results of the present study suggest that episodic releases of LH occur during anoestrus and periods of low luteal activity. The fluctuations in LH levels, as observed during the period of low luteal activity, i.e. before Day \m=-\25 of anoestrus, were less pronounced during the periods of high luteal activity. The view that luteal activity precedes the first behavioural oestrus of the breeding season is supported.

No abstract

Changes in profiles of serum luteinizing hormone (LH), follicle stimulating hormone (FSH) and testosterone and in mating performance and ejaculate volume have been determined in Finnish Landrace (Finn)and Managra Synthetic (Line-M) rams during the ovine breeding season. In early August, mid-September, early November and mid-December four rams of each breed were bled by venipuncture from the jugular vein at 20-min intervals for two 8-hr periods. Rams were bled while in the absence (control period) and presence (mating period) of ewes in estradiol-induced estrus. An ejaculate was also collected from either five or six of the rams during these months. Aliquots of serum were assayed for LH, FSH and testosterone by radioimmunoassay. Testosterone concentrations in seminal plasma were also determined.Episodic increases in serum levels of LH and testosterone were evident in all rams during each 8-hr period, while FSH fluctuated very little from baseline concentrations (usually