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Search for other papers by PATRICIA W. MAJOR in
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Search for other papers by D. T. ARMSTRONG in
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SUMMARY
Small doses of luteinizing hormone (LH) have been shown to exert a stimulating effect on the in vitro carbohydrate metabolism of the prepubertal rat ovary. In order to determine the specificity of the response, studies were undertaken comparing the effects caused by LH with those of other anterior pituitary hormones. Preparations of thyroid stimulating hormone (TSH) caused responses similar to those caused by LH, when added to the media in which prepubertal rat ovaries were incubated. A detailed study of the effects of TSH preparations (prepared by different procedures with known low levels of LH contamination) on lactic acid production, has been undertaken. All TSH preparations tested caused considerably greater stimulation of glycolysis than could be accounted for on the basis of their contamination with LH when the latter was appraised by the ovarian ascorbic acid depletion assay.
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The weights, protein concentrations, and concentrations of cyclic AMP and cyclic GMP in the ovaries of prepubertal rats have been measured after induction of follicular growth by administration of pregnant mare serum gonadotrophin (PMSG). Three phases of ovarian growth, the follicular growth phase, the preovulatory phase and the luteal phase were investigated. Ovulation was induced by administration of human chorionic gonadotrophin (hCG). During the follicular phase, ovarian weight, protein content and the content of both cyclic AMP and cyclic GMP increased 2–3 days after administration of PMSG. Administration of hCG 65 h after PMSG caused a rapid rise in the concentration of cyclic AMP but the concentration of cyclic GMP tended to fall. During the luteal phase the concentrations of both cyclic nucleotides decreased.
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Search for other papers by PATRICIA W. MAJOR in
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SUMMARY
Concentrations of cyclic AMP were measured in rabbit ovaries at various times after injection of an ovulatory dose of human chorionic gonadotrophin (HCG). A biphasic increase in cyclic AMP concentration occurred during the preovulatory period, with peaks 30 min and 3–4 h after HCG injection. Concentrations of cyclic AMP had returned to those observed in ovaries of control oestrous animals before the onset of ovulation 10–12 h after administration of HCG, and remained low throughout the period of pseudopregnancy. Concentrations of cyclic AMP in the newly formed and developing corpora lutea were similar to the concentrations observed in the remainder of the tissue during this period. No significant increase in cyclic AMP concentration was observed 7–9 days after initiation of ovulation. Concentrations of ATP were also investigated during the preovulatory period. The dose– response relationship of HCG to cyclic AMP production in oestrous rabbit ovaries was investigated.
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Search for other papers by PATRICIA W. MAJOR in
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SUMMARY
The effects of NADPH, NADP+, succinate and cyclic AMP on progestational steroid synthesis have been investigated in subcellular fractions of rabbit interstitial tissue. Production of progesterone and 20α-hydroxy-4-pregnen-3-one increased during incubation of mitochondria with NADPH and NADP+ respectively, and an increase in 20α-hydroxy-4-pregnen-3-one was observed after incubation of microsomes with NADP+. No changes in progestational steroid production were observed in individual cell fractions after incubation with cyclic AMP or succinate. However, a small but significant increase in progesterone synthesis occurred in a combined fraction containing mitochondria, microsomes and cytosol when incubated with cyclic AMP.
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Search for other papers by R. KILPATRICK in
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SUMMARY
The role of cyclic AMP in the mediation of hormone action is reviewed, including information available from 1958–1971. Evidence for its involvement in each hormone action is considered separately. The known mechanisms by which cyclic AMP stimulates specific metabolic processes are also described. Other speculations on the role of cyclic AMP in the mediation of hormone action are discussed.
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Search for other papers by PATRICIA W. MAJOR in
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SUMMARY
Rabbit ovarian homogenates were incubated in Krebs—Ringer bicarbonate buffer with or without glucose in the presence of citric acid cycle intermediates, α-glycerophosphate and lactic acid. The effects of these compounds on steroid synthesis were then observed. The inclusion of glucose alone in the medium was sufficient to increase progesterone biosynthesis. Succinate stimulated total progestational steroid synthesis both in the presence and absence of glucose in the medium, while citrate had an inhibitory effect in both cases. Malate stimulated synthesis only in the absence of glucose, while oxaloacetate and α-glycerophosphate stimulated synthesis only when glucose was present in the medium. Lactic acid had no effect in the absence of glucose, but significantly inhibited synthesis when glucose was present in the medium.
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Search for other papers by PATRICIA W. MAJOR in
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SUMMARY
Luteinizing hormone and cyclic AMP stimulate synthesis of progestational steroids in rabbit ovarian homogenates. Both progesterone and 20α-hydroxypregn-4-en-3-one are produced and, in contrast to ovarian slice preparations, progesterone is the predominant steroid formed.
Steroid synthesis in homogenates from interstitial tissue is stimulated to a greater extent than in homogenates of luteal tissue. Synthesis of these steroids by the homogenates can also be increased by addition of NADP+ and NADPH. The amount and nature of the steroid synthesized varies with the amount of cofactor added and with its form (oxidized or reduced). When both forms of cofactor were added to the system in vitro, the ratio of the oxidized to the reduced form appeared to be important in determining the form of the steroid produced.
Search for other papers by ELISABETH HORRELL in
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Search for other papers by R. KILPATRICK in
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Search for other papers by PATRICIA W. MAJOR in
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Two pituitary hormones, luteinizing hormone (LH) and prolactin, influence the steroid synthetic capacity of ovarian tissue in several species (Greep, 1971). Prolactin increases cholesterol content of rabbit interstitial tissue (Hilliard, Spies, Lucas & Sawyer, 1968), while LH increases the synthesis of progestational steroids from cholesterol (Dorrington & Kilpatrick, 1966; Solod, Armstrong & Greep, 1966). Adenosine 3′,5′-monophosphate (cyclic AMP) has been implicated as an intermediate in the action of LH in the ovary (Hall & Koritz, 1965; Marsh, Butcher, Savard & Sutherland, 1966; Dorrington & Kilpatrick, 1967) and theophylline, an inhibitor of cyclic nucleotide phosphodiesterase, increases the effect of LH on steroidogenesis in vitro. Much of the evidence implicating cyclic AMP as a mediator of hormone action has been obtained from experiments in vitro and very large amounts of cyclic AMP or derivatives are necessary to alter metabolic activity in vivo (Levine, 1970). In order to investigate the possibility of regulating
Search for other papers by ELISABETH HORRELL in
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Search for other papers by PATRICIA W. MAJOR in
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Search for other papers by R. KILPATRICK in
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Search for other papers by BRENDA M. SMITH in
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SUMMARY
The secretion of progestational steroids by the rabbit ovary was examined during pseudopregnancy. Progesterone secretion rose up to the mid-period but exceeded secretion of 20α-dihydroprogesterone only on days 7 and 9. The development of the corpus luteum and interstitial tissue and their content of progestational steroids were also examined during this period. The progesterone content of corpus luteum tissue fell towards the end of pseudopregnancy, while the corpora lutea remained large. Levels of 20α-dihydroprogesterone were generally higher in the interstitial tissue after the first few days. A significant alteration in the pattern of steroid synthesis and secretion occurred at a time corresponding to the period of implantation in the pregnant rabbit.
