Plasma and pituitary luteinizing hormone and peripheral plasma oestradiol concentrations in the normal oestrous cycle of the rat and after experimental manipulation of the cycle

Plasma and pituitary luteinizing hormone (LH) concentrations were measured by radioimmunoassay at different stages of the normal 4- and 5-day oestrous cycle of rats. Plasma levels were low except between the afternoon of pro-oestrus and the morning of oestrus when levels were high but variable. Pituitary LH content and concentration were less consistent but averaged values showed a steady rise from a low level after ovulation to a peak on the afternoon of pro-oestrus, and a rapid fall that evening when plasma levels rose rapidly.

No significant differences were observed in plasma LH between 4- and 5-day cycles; in particular there was no reduction at metoestrus or dioestrus-1 or increase on the evening of dioestrus-2. Plasma oestradiol was already high on the morning of dioestrus-2 in some rats and in all rats by that evening. On the morning of pro-oestrus in the 5-day cycle, plasma oestradiol was still high but somewhat lower than at the corresponding stage in the 4-day cycle.

Blocking ovulation by administration of sodium pentobarbitone at prooestrus in a 4-day cycle prevented the rise in plasma LH and the fall in pituitary content. Blocking generally failed in animals whose plasma LH had reached the level of 20 ng/ml or more at the time of injection. Plasma oestradiol levels on the morning of the expected day of oestrus were higher than normal in animals in which ovulation was blocked by pentobarbitone but were below pro-oestrous values. In the anovulatory state induced by exposure to constant light no major increase in plasma LH was detected after 24 days of illumination or after 3 months exposure. Animals rendered anovulatory by injection of testosterone propionate on the 4th day of postnatal life had low plasma LH levels as adults. All three groups had a low pituitary LH content. The animals exposed to long-term light and those treated with androgen generally had plasma oestradiol concentrations below the peak levels seen on the morning of pro-oestrus in the normal cycle.

Plasma and pituitary luteinizing hormone concentrations and peripheral plasma oestradiol concentration during early pregnancy and after the administration of progestational steroids in the rat

Plasma luteinizing hormone (LH) concentrations were already lower on Day 2 of pregnancy than at the same time after the preceding ovulation in the non-pregnant rat, and fell progressively up to Day 16 of pregnancy. No evidence was obtained of any increase at the time when the ovulatory surge of LH would have occurred if the animal had not become pregnant. Pituitary LH concentration was lower in mated rats on the morning of Day 0 of pregnancy than in unmated controls on the morning of the day of oestrus. Subsequently it increased slowly to reach a level higher than at any stage of the oestrous cycle by Day 8 of pregnancy and remained high until at least Day 16 of pregnancy. Peripheral plasma oestradiol concentration increased late on Day 2 of pregnancy and was still raised on Day 4 but was never more than about one fourth of the peak concentration seen on the morning of prooestrus during the oestrous cycle. There were similar changes in plasma LH and oestradiol concentrations in the 48 h after a single injection of 2·5mg progesterone on the morning of the day of dioestrus, a procedure that delays ovulation by 1 or 2 days. Administration of a synthetic progestational compound (medroxyprogesterone acetate) to pregnant rats delayed blastocyst implantation and the delay was associated with a marked decrease in peripheral plasma LH to levels below those of normal pregnancy.

Changes in gonadotrophins, ovarian steroids and follicular morphology in sheep at oestrus

The concentrations of progesterone, oestrogen and luteinizing hormone (LH) in ovarian venous plasma, and of progesterone, follicle-stimulating hormone, LH and prolactin in peripheral plasma were measured in 47 Welsh Mountain sheep at accurately timed stages around oestrus. The histology and ultrastructure of the pre-ovulatory and newly ruptured follicles in these animals were also examined.

The highest ovarian vein levels of oestrogen were invariably obtained from the ovary containing the largest non-atretic follicle. A significant amount of oestrogen was already being secreted by day 13, when both the peripheral and ovarian venous blood progesterone levels were still high.

On day 15 the corpus luteum stopped secreting progesterone; coincident with this decline there was a maximal increase in oestrogen secretion from the largest non-atretic follicle. The thecal cells of this follicle enlarged concomitantly with the rise in oestrogen, and maximal development of the smooth endoplasmic reticulum was observed at or after the oestrogen peak.

By 6 h after the onset of oestrus, progesterone concentration was still very low, and oestrogen values had fallen in most animals, while LH showed a pronounced increase. The maximal level of prolactin was also found at this time.

By 15 h after the onset of oestrus, both progesterone and oestrogen values were low and LH had returned to baseline levels except in a few animals. Ovulation had occurred in 11 out of 12 animals by 30 h after the onset of oestrus and the recently ruptured follicle was just beginning to secrete a little progesterone. Luteinizing hormone and oestrogen values were very low.

Relationship between blood levels of luteinizing hormone and testosterone in bulls, and the effects of sexual stimulation

Luteinizing hormone (LH) and testosterone were measured in the peripheral plasma of two bulls by radioimmunoassay and competitive protein binding techniques. Samples were collected from an indwelling jugular catheter once an hour for 24 h, and then at more frequent intervals after a number of experimental procedures.

Each bull showed its own characteristic pattern of cyclic LH changes, with 5–10 peaks during 24 h that were apparently unrelated to daylight, feeding or sleep. Each LH peak was associated with a testosterone peak; the LH concentrations ranged from 5 to 50 ng/ml, and those of testosterone from 2 to 20 ng/ml.

Sexual stimulation, such as the sight of a cow, or 'teasing', or on one occasion the act of ejaculation itself, caused an immediate release of a large amount of LH. If the testosterone levels were low at the time, the LH peak was followed by a testosterone peak. But when the testosterone levels were high at the time of LH discharge, the testis seemed to be unable to respond any further. An intravenous injection of 500 i.u. human chorionic gonadotrophin was associated with LH release and caused the testosterone levels to rise to maximal values of 22 ng/ml within 1½ h.

It is concluded that the cyclical pattern of LH release is due to some inherent central rhythm, and that each transient LH peak results in transient maximal stimulation of testicular testosterone secretion.

Assay of 17beta-oestradiol by competitive protein binding methods

This report gives details of the authors' procedure for the measurement of 17β-oestradiol in plasma by competitive protein binding analysis, together with the results of studies on various parameters of the assay system. The preparation of the receptor cytosol, the assay system, extraction of plasma and reliability criteria are all discussed. The procedure is compared with those reported by other workers. Finally the results obtained by this technique are compared with those obtained by other methods and current applications are presented.