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Biomedical subjects

P J Sharp

Publications and source records attributed to P J Sharp.

At least 199 records · Page 11Linked to original sources
PubMed1976

Induction of luteinizing hormone release by gonadal steroids in the ovariectomized domestic hen.

The ability of intramuscular injections of gonadal steroids to exert a positive feedback action on LH secretion was investigated in the ovariectomized hen. Plasma LH was measured by radioimmunoassay. Single injections of progesterone (dose range: 0.05-10 mg/kg) or oestradiol benzoate (dose range: 0.01-1 mg/kg) did not result in an increase in plasma LH concentration. After priming with 0.1 mg oestradiol benzoate/kg on alternate days for 7 days and with 0.5 mg progesterone/kg on days 5, 6 and 7, a single injection of progesterone on day 8 (dose range: 0.1-2 mg/kg) caused the plasma LH concentration to start increasing after 15 to 30 min. Peak LH concentration was reached around 1.5-2 h after injection. The magnitude of LH response to progesterone was dose related. In contrast, a single injection of oestradiol benzoate (dose range: 0.01-1 mg/kg) failed to stimulate LH release in the oestrogen-progesterone primed ovariectomized (O-P-OVX) hen. A single injection of testosterone (dose range: 0.1-2.0 mg/kg) failed to stimulate LH release in ten out of 12 O-P-OVX hens. A small increase in LH secretion was observed in the two remaining birds. When oestrogen or progesterone was omitted from the priming schedule, a LH positive feedback response to a single injection of progesterone was not observed. Increasing or decreasing the mount of oestrogen or progesterone in the priming schedule modified the LH response to a single injection of progesterone on the day following the last priming injection. This suggested that a critical oestrogen to progesterone ratio was required to prime the LH positive feedback mechanism. It is suggested that, in the hen, the release of LH is facilitated by the positive feedback effect of a combination of oestrogen and progesterone in a two-phase process. The first is the priming phase, which depends on the presence in the blood of oestrogen and progesterone; the second is the ind .uctive phase, which depends only on an incremental change in plasma progesterone concentration. Oestrogen is not involved in the induceive phase.

Animals↗
PubMed1975

Immunofluorescent localization of sites binding anti-synthetic LHRH serum in the median eminence of the greenfinch (Chloris chloris L.).

With an indirect immunofluorescence technique and an antiserum raised against synthetic LHRH, immunofluorescent granules were observed in fine radially oriented fibres in the palisade layer of the zoma externa in both the anterior and the posterior divisions of the median eminence in the greenfinch. There was no specific immunofluorescence in the tractus supraoptico-hypophyseus. It is concluded that the greenfinch median eminence contains material which is similar to mammalian LHRH.

Animals↗
PubMed1975

Annual cycle of plasma luteinizing hormone concentrations in wild mallard drakes.

Plasma LH concentrations were followed in 9 individually marked wild mallard drakes in Kiel (54 degrees N) for one year at monthly intervals. Mean LH levels increased during the spring and reached the annual maximum in April and May. In June when testicular regressions occurs, the LH titer sharply decreased and was lower than at any other phase of the annual cycle. In late fall mean plasma LH concentrations increased and, whilst not reaching the values observed during the breeding season, remained relatively high during the winter. Thus, in the mallard LH can be released under short and long daily photo-periods.

Animals↗
PubMed1975

Seasonal changes in plasma LH levels in domestic ducks.

Seasonal changes in plasma LH concentrations were measured by radioimmunoassay every month for 1 year in nine Khaki Campbell drakes kept under natural lighting conditions in Kiel, Germany. The LH levels rose in all the birds in March and April and reached a mean (+/-S.E.) maximum of 2-4 +/- 0-2 ng/ml early in May. Thereafter, LH levels remained high in three drakes, but decreased in the other six to between 0-9 and 0-4 ng/ml early in June and/or July and rose to about 2-5 ng/ml by the beginning of August. Plasma LH levels started to fall in all nine drakes in September and by early October had reached winter values of about 1-2 to 1-5 ng/ml. A small transient increase in the level of circulating LH was observed in most drakes during November or December.

Animals↗
PubMed1975

Episodic release of luteinizing hormone in the domestic fowl.

Plasma luteinizing hormone (LH) levels were measured by radioimmunoassay in serial samples taken from intact adult cockerels, gonadectomized fowl of both sexes and laying hens. By sampling at 30 and 10 min intervals, it was shown that in cockerels LH is released episodically. Each secretory episode lasted 90-120 min and was characterized by a 100-200% rise in LH levels over a period of 10-15 min followed by a more gradual, exponential decline. Mean plasma LH levels were found to be depressed in cockerels as a result of the handling associated with taking blood samples; in cases where LH levels were most depressed, an episodic pattern of secretion could not be demonstrated. In the gonadectomized fowl, an episodic pattern of LH secretion was shown when blood samples were taken at 10 or 5 min intervals. During each secretory episode, which lasted 20-45 min, LH levels rose by 20-60%. It is suggested that the increase in mean plasma LH levels in gonadectomized fowl (30-77 ng/ml) over those in cockerels (7-16 ng/ml) is related to an increase in the frequency of the episodic release of the hormone. Episodic discharges of LH could not be demonstrated in laying hens. In these birds the mean LH levels are low (1-5--2-4 ng/ml) and consequently may be maintained by secretory episodes which are of too low an amplitude to be detectable.

Animals↗
PubMed1975

A comparison of variations in plasma luteinizing hormone concentrations in male and female domestic chickens (Gallus domesticus) from hatch to sexual maturity.

Changes in plasma LH concentrations were followed in chickens of both sexes from hatch to sexual maturity using a radioimmunoassay. Mean levels of LH were lower in the females than in the males at all stages of development. These levels rose rapidly in both sexes during the first week after hatch to maxima of 6-5 +/- 1-2 (S.E.M.) ng/ml (n = 6) in the males and 4-6 +/- 0-6 ng/ml (n = 6) in the females. Thereafter levels of the hormone in the circulation stabilized in the males but fell over a period of 1 or 2 weeks in the females to 2-5-3 ng/ml. Plasma LH levels started to rise steeply in both sexes when they were between 16 and 19 weeks old at the same time as there was an increase in the rate of comb growth. Afterwards in six of the males studied in detail the mean plasma LH level rose significantly (P less than 0-01) over a period of 5-8 weeks from 8-1 +/- 1-2 to 13-2 +/- 1-9 ng/ml. In a parallel study on six females the rate of LH secretion increased for approximately 3 weeks and then decreased for about the same period forming a prepubertal LH peak. The first eggs were laid between 22 and 25 weeks of age when mean plasma LH levels had fallen to about 1-8 ng/ml. The mean plasma LH level in these hens when they were laying (1-8 +/- 0-3 ng/ml) was significantly lower (P less than 0-01) than when they were sexually immature (2-7 +/- 0-3 ng/ml). The duration of the period of rapid comb growth in each bird was closely related in the males to the time during which prepubertal LH peak. Differences in mean plasma LH concentrations in individual birds of either sex before the onset of puberty appeared to be related to subsequent reproductive performance.

Age Factors↗
PubMed1975

Effects of progesterone and synthetic luteinizing hormone releasing hormone on the release of luteinizing hormone during sexual maturation in the hen (Gallus domesticus).

Single intramuscular injections of 0-5 mg progesterone/kg resulted in increased LH secretion in laying hens but not in pullets with completely undeveloped sexual organs. Injections of the steroid were first able to stimulate LH release 8-10 weeks before the onset of lay when the comb, ovary and oviduct had started to grow and basal plasma LH concentrations were beginning to rise. At this time, injecitons of 10 mug synthetic LH-RH/kg resulted in an incremental change in plasma LH levels of around 26 ng/ml. A similar incremental change was observed after giving the same dose of LH-RH to pullets with no signs of sexual development. Three to four weeks before the first eggs were laid, basal plasma LH levles started to fall, the pituitary became progressively more insensitive to synthetic LH-RH and injections of 0-5 mg progesterone/kg resulted in a reduced LH response. Ten mug LH-RH/kg caused incremental changes in blood levels of LH of less than 5 ng/ml. The final stage of sexual maturation occurred during the week before the onset of lay and was characterized by a rapid growth of large yolky ovarian follicles and a further fall in the sensitivity of the pituitary to synthetic LH-RH. However, injections of 0-5 mg progesterone/kg resulted in a prolonged release of LH. These observations are discussed in relation to the maturatio of the positive feedback mechanism by which progesterone stimulates the secretion of LH.

Animals↗
PubMed1975

Changes in plasma concentrations of luteinizing hormone after injection of progesterone at various times during the ovulatory cycle of the domestic hen (Gallus domesticus).

Changes in plasma LH concentrations after i.m. injections of 0-5 mg progesterone/kg at various stages of the ovulatory cycle were measured by radioimmunoassay. Four types of response were observed. (1) When the steroid was injected between 4 h after and 12 h before an ovulation, LH levels started to rise after 15--45 min and reached peak values within 90--120 min. The mean maximal incremental change in the level of LH was 1-58 +/- 0-10(S.E.M.) ng/ml (n = 37). (2) In contrast, when progesterone was injected 12--8 h before ovulation, i.e. immediately before a spontaneous pre-ovulatory LH surge, the resulting mean maximal incremental change in LH level, 0-79 +/- 0-12 ng/ml (n = 9), was significantly smaller (P less than 0-001). (3) If progesterone was injected 8--4 h before ovulation, i.e. when pre-ovulatory LH levels were rising, they immediately started to rise more rapidly and reached peak values within 45 min. The maximal incremental change in the level of LH under these circumstances, 2-34 +/- 0-20 ng/ml (n = 12), was significantly greater (P less than 0-001) in both cases) than the changes observed in the responses 1 and 2 described above. (4) Levels of LH generally showed no incremental change in response to injections of progesterone given 4--0 h before ovulation, i.e. when pre-ovulatory LH levels were falling. It was concluded that the type of change in plasma LH levels induced by progesterone depended upon the stage of the ovulatory cycle at which the steroid was injected.

Animals↗