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SUMMARY
The effects of oestrogens, testosterone, thyroxine, avian and mammalian gonadotrophins and of fasting, on the plasma free fatty acid (FFA) levels in the domestic fowl were investigated. Oestrogen treatment increased the levels of plasma FFA simultaneously with those of the total lipids and lipophosphoprotein in the immature fowl. Testosterone and thyroxine decreased the levels of plasma lipids and of lipophosphoprotein in the laying fowl, but had no effect upon the levels of plasma FFA in either the immature or laying fowl. Gonadotrophins were without effect upon the plasma FFA in the immature pullet but increased the levels in laying or moulting birds, the increases being accompanied by marked follicular growth. Fastings increased the level of plasma FFA in immature birds, but decreased the levels of FFA and total lipid in laying birds. Injections of large doses of hog anterior pituitary extract were without effect on the plasma FFA in conscious immature pullets but induced marked increases in the plasma FFA and a gross lipaemia in the rabbit. It is considered that the increases in plasma FFA found when the bird comes into lay are an indirect result of ovarian stimulation by pituitary hormones.
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Luteinizing hormone (LH) is commonly determined by the depletion of ascorbic acid in the ovaries of rats pretreated with gonadotrophins (OAAD) (Parlow, 1961). Recently a method involving the depletion of ovarian cholesterol has been reported (Bell, Mukerji & Loraine, 1964). Attempts to establish this method in our laboratory have not met with success.
Rats, bred from the colony maintained by the M.R.C. Unit for Clinical Endocrinology, Edinburgh, were housed in windowless rooms at a mean temperature of 72°. Two main lines were established: one maintained on the Ceru rat diet (McGregor and Co. (Leith) Ltd., identical with that used by the Edinburgh investigators), the other maintained on Oxoid Rat Diet 18B. The system of management and selection was similar to that used by the Edinburgh workers. Rats selected for age and body weight were pretreated as described by Bell et al. (1964). Cholesterol was determined as described by these authors
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SUMMARY
The level of plasma free fatty acids (FFA) in both laying and immature non-laying hens was not markedly decreased by intravenously injected amounts of glucose sufficient to double the level of plasma glucose for 15–30 min. This was true for fasting and for fed birds. Adrenocorticotrophic hormone (ACTH) given i.v. to laying birds produced a definite increase in the levels of plasma FFA and glucose in doses of 60 i.u./kg. Daily doses of long-acting ACTH given i.m. for 3 days to laying birds produced a marked increase in plasma glucose accompanied by a pronounced fall in plasma FFA. Insulin markedly lowered the plasma glucose level in both mature and immature birds and caused a large and immediate increase in plasma FFA. Glucagon also induced a marked increase in plasma FFA accompanied by a rise in plasma glucose. The effects of insulin and glucagon were not abolished by pretreating the birds with reserpine or hexamethonium bromide. It is concluded that the effect of glucagon on plasma FFA is probably a result of a direct action on avian adipose tissue and that insulin may promote a similar response by an increased release of glucagon from the pancreas.
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SUMMARY
Measurement of the uptake and retention of a radioactive post-coital antifertility agent tamoxifen, by reproductive tissues of the rat have shown that the ovary retained more radioactivity than did any other reproductive organ. Studies have also been made of the uptake and distribution of [3H]tamoxifen and [3H]oestradiol-17β in the uterus of the pregnant rat on days 2–6 post coitum. Twenty-four hours after administration of tamoxifen, either i.v. or orally, 40–50% of the radioactivity was in the high speed pellet, 10–20% in the nuclear fraction, and 15–30% in the cytosol. An equivalent dose of [3H]oestradiol-17β yielded distributions of 5%, 5% and 82% respectively. Fractionation of uteri from animals given 0·2 mg tamoxifen/kg on Day 2 of pregnancy followed by [3H]oestradiol 60 min before death showed little difference in total uptake of oestradiol or distribution in the subcellular fraction on Days 4, 5 and 6. Although uptake of oestradiol by uterine nuclei was reduced on Day 3 by previous administration of tamoxifen on Day 2, appreciable quantities were still bound to the nuclear receptors. Treatment of ovariectomized animals with tamoxifen at doses up to 40 μg/rat (i.e. 0·2 mg/kg) led to the accumulation of oestrogen–receptor complex in the nucleus.
It is concluded that the antifertility properties of tamoxifen (under the conditions of these experiments) cannot be ascribed to the suppression of uptake and binding of oestradiol by the uterus.
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SUMMARY
The quantities of luteinizing hormone (LH) in the pituitary glands of the domestic fowl have been measured during an ovulatory cycle using the method of ovarian ascorbic acid depletion. Extracts of avian anterior pituitary were qualitatively similar to a standard preparation of HCG in this test and the activity was destroyed by treatment with urea.
During the ovulatory cycle the levels of LH in the pituitary underwent two major changes, being high at the point of ovulation, falling and remaining low for 6 hr. after ovulation and then rising to a second peak 8 hr. before the next ovulation. The levels decreased rapidly and remained low until at least 2 hr. before ovulation. It is suggested that the variations in pituitary LH content are the result of suppression of release by ovarian hormones produced by the maturing follicles.
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SUMMARY
Plasma levels of oestradiol-17β, progesterone and luteinizing hormone (LH) and pituitary levels of LH have been measured during the first 6 days of pregnancy, in normal rats and in rats receiving two doses of Tamoxifen (trans-1-(p-β dimethylamino-ethoxyphenyl)-1-2 diphenylbut-1-ene) on day 2 of pregnancy.
In normal rats oestradiol rose strongly from early on day 3 to reach a peak concentration between 22.00 h on day 3 and 08.00 h on day 4. Progesterone concentrations rose from day 2 to reach peak values on day 3–4. In animals in which implantation was delayed 20–24 h by administration of Tamoxifen (0·1 mg/kg) orally on day 2 the increased level of plasma oestrogen was also delayed by 20 h. A higher dose of Tamoxifen (0·2 mg/kg) on day 2, which prevented implantation, completely eliminated the increase in plasma oestradiol. Neither dose of Tamoxifen affected the levels of progesterone.
In both normal rats and rats treated with 0·1 mg Tamoxifen/kg, plasma LH levels declined by day 3 while pituitary levels rose steadily. There was no detectable change in either plasma or pituitary LH levels, accompanying the increase in plasma oestradiol in the normal rats. In animals receiving Tamoxifen (0·2 mg/kg), plasma LH increased to a maximum by day 4 while levels of pituitary LH decreased.
The results show that the oestrogen ' surge' of early pregnancy, occurs normally about midnight on day 3 and not late on day 4 as previously thought. It is considered that the plasma oestradiol peak in early pregnancy results from an increased release of FSH rather than an increased release of LH. Tamoxifen may owe part of its antifertility action to a capacity to inhibit the synthesis of oestradiol from progesterone.
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SUMMARY
The luteinizing hormone (LH) content of the anterior pituitary of the domestic fowl has been determined at different times during the interval between successive clutches of eggs. The LH content remained constant for 12–14 hr. after the ovulation of the last egg of the sequence, decreased 16 hr. before ovulation, rose again to a peak 12 hr. before ovulation and decreased to lower levels 4 and 8 hr. before the ovulation itself, at which point levels had risen to the normal values. These changes are discussed in relation to the lighting sequence and times of oviposition. It is suggested that the decreased levels 4–8 hr. before ovulation represents the release of ovulatory LH.
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SUMMARY
Groups of laying mature domestic fowl were injected i.m. with varying doses of either oestradiol benzoate, testosterone propionate or progesterone and were killed at random intervals throughout the day without reference to any specific point in the ovulatory cycle. Luteinizing hormone (LH) was assayed in the anterior pituitaries of each group. It was shown that oestradiol in doses calculated to be equal to or above the physiological level, increased pituitary LH without necessarily affecting the laying cycle. Testosterone had no significant effect on pituitary LH, while progesterone significantly increased pituitary LH at doses which had no apparent effect upon ovulation. Doses effective in the laying hen had little or no effect on the pituitary content of LH in immature birds. The results in the laying hen are in harmony with the concept previously proposed, by which changes in the levels of circulating plasma oestrogens may regulate the ovulatory pattern of the fowl by inhibiting release of pituitary LH.
