Ian P. Callard

Hormones and reproduction in the female lizard Sceloporus cyanogenys

Abstract The reproductive cycle and the effects of various endocrine manipulations thereon are described for the female iguanid lizard Scelporus cyanogenys . Although castration reduced oviduct weight in nonpregnant animals, the operation had no effect upon pregnancy. Estradiol injections significantly increased oviduct weight in castrate nonpregnant animals. Injection of PMS early in the ovarian growth cycle markedly accelerated gonadal development, oviduct and liver growth. However, PMS injections did not induce a second ovarian cycle when administered after parturition. While injections of progesterone alone did not alter reproductive parameters, injection of the steroid at the same time as PMS cutailed all the stimulatory effects of PMS. Injections of either progesterone or prolactin alone were effective in inhibiting ovulation and oviduct growth when administered to animals which had well developed ovaries (mid-vitellogenic). Further, progesterone was more effective than prolactin in ovulation inhibition. Intrahypothalamic implants of progesterone had no effect on ovulation or ovarian growth, but intrahypothalamic implants of estrogen inhibited ovulation and to a certain extent oviduct growth; however, estrogen implants did not influence ovarian growth. All animals treated with estrogen had elevated liver weights and serum protein levels.

Recent studies on the control of the reptilian ovarian cycle

Abstract As a working hypothesis the following sequence of events may be considered in the control of the gonad in Sceloporus: (1) Under the influence of environmental cues, the secretion of gonadotropin(s) from the anterior lobe is elicited and follicular development and steroid secretion begin. (2) Estrogen secreted by the ovary acts (a) to stimulate the production of growth hormone, (b) in concert with growth hormone on the liver to induce vitellogenesis and the production of lipophosphoprotein which is accumulated by the ovary resulting in rapid ovarian growth, and (c) via the hypothalamus to depress ovulatory quantities of gonadotropin(s). (3) Rising levels of progesterone may facilitate ovulation by inhibiting gonadotropin and/or estrogen production followed by a gonadotropin surge. (4) Following ovulation, progesterone is produced in large quantities by the corpus luteum controlled by pituitary hormones and prevents further follicular development by acting directly on the hypothalamus and possibly at the peripheral level to antagonize vitellogenesis for the duration of gestation and for a period postpartum. (5) Prolactin may be involved in a feedback loop with progesterone, producing antivitellogenic effects similar to progesterone. (6) Following parturition, plasma levels of progesterone decrease slowly as the corpus luteum involutes. The following fall, in response to changing environmental conditions, the onset of gonadal growth begins again.

A histochemical study of ovarian function in the ovoviviparous elasmobranch, Squalus acanthias

Abstract Ovarian tissues from the ovoviviparous elasmobranch, Squalus acanthias were examined histochemically for the distribution of NAD and NADP diaphorase, glucose-6-phosphate dehydrogenase (G-6-PDH), 3 beta hydroxysteroid dehydrogenase (3βHSD), 3 alpha hydroxysteroid dehydrogenase (3αHSD), 17 beta hydroxysteroid dehydrogenase (17βHSD), and 20 beta hydroxysteroid dehydrogenase (20βHSD). The histochemical distribution of the enzymes was correlated with the histological picture obtained from contiguous sections. NAD, NADP diaphorase, and G-6-PDH were distributed throughout the ovary and positive reactions were obtained in all tissues tested. 3βHSD activity was demonstrated in the granulosa of follicles at various stages of development, increasing in intensity as the follicle matured. After ovulation, 3βHSD was found in the post-ovulatory follicle (“corpus luteum”). No 3βHSD activity was observed in atretic follicles (“preovulatory corpora lutea”). 3αHSD was only observed as a weak reaction in the granulosa of late preovulatory follicles, and no activity of 17βHSD and 20βHSD was observed in any ovarian component tissues.

Reproduction and estrogen-induced vitellogenesis in Dipsosaurus dorsalis.

1. n1. The ovarian cycle of female Dipsosaurus dorsalis was studied during June through October. A peak of vitellogenesis occurred in late June. n n2. n2. Ovarian maturation was accompanied by significant increases in oviduct weight, plasma protein fraction 4 (the “beta-globulin”) and total plasma calcium. n n3. n3. Ovulation was followed first by a decrease in calcium and later by a decrease in plasma fraction 4. n n4. n4. Oviduct and adrenal weight decreased from peak summer levels by October. n n5. n5. A single injection of estradiol 17β in post-reproductive females was followed by significant increases in plasma protein fraction 4 and calcium. n n6. n6. This response did not occur in the absence of the pituitary gland.

Plasma corticosterone levels in the male iguanid lizard Sceloporus cyanogenys under various physiological conditions

Variations in peripheral plasma corticosterone levels in male iguanid lizards, Sceloporus cyanogenys, were investigated under varying physiological conditions. Control baseline levels of the steroid in plasma were significantly decreased by hypophysectomy, adrenalectomy, hypothalamic lesions, and cyanoketone, an inhibitor of Δ5-3β hydroxysteroid dehydrogenase. Levels were increased following treatment with mammalian ACTH in both intact and hypophysectomized lizards. In the intact animal, ACTH produced a more rapid, more prolonged, and quantitatively greater response of the adrenal gland than the same hormone when administered to the hypophysectomized animal. An apparent increase in corticosterone levels was observed following metyrapone (an 11β-hydroxylase inhibitor) treatment, and aminoglutethimide, an inhibitor of the formation of pregnenolone from cholesterol, had no effect.

Observations on the water and electrolyte composition of the iguanid lizard Dipsosaurus dorsalis (Baird & Girard), with special reference to the control by the pituitary gland and the adrenal cortex ☆

Abstract The distribution of water and electrolytes in the extracellular and intracellular composition of the reptile Dipsosaurus dorsalis (Baird & Girard) was examined. Hypophysectomy (12 days) caused adrenocortical atrophy, rise in plasma water and Na + concentration, told muscle water, and intracellular Na + concentration and decline in intracellular K + concentration. Ca 2+ and Mg 2+ levels in plasma and muscles were unaffected. ACTH injected into hypophysectomized lizards prevented adrenocortical changes but had little effect on electrolyte composition. Given singly, corticosterone prevented rise in plasma water and caused by a drop in muscle water content. However, when corticosterone and prolactin were administered together, plasma and muscle composition was rendered normal. Injection of aldosterone in addition to the last two hormones caused Na + retention and K + and Mg 2+ loss.

Effects of intrahypothalamic betamethazone implants on adrenal function in male Sceloporus cyanogenys

Male S. cyanogenys were appropriately treated with Metopirone, an 11 beta hydroxylase enzyme inhibitor, thus blocking the synthesis of adrenal steroids. This treatment caused a highly significant increase in adrenal weight (controls 6.61 ± .49 mg/100 gm vs 10.58 ± 1.04 mg/100 gm, p < .001). Prior (30 days) stereotaxic implantation of a synthetic corticoid, betamethazone, in the hypothalamus, not only prevented this compensatory adrenal hypertrophy but reduced adrenal size below that of controls to 4.60 ± .19 mg/100 gm (p < .001). Blank hypothalamic implants and subcutaneous implants of betamethazone were without effect, indicating that the operative procedure itself did not cause hypertrophy nor was the steroid implanted in the hypothalamus acting systemically. While the possibility that the effects noted may be mediated at the adeno-hypophyseal level has not been eliminated, the data suggest that the hypothalamus of S. cyanogenys contains steroid-sensitive receptor cells which control adrenal size via the anterior pituitary gland.

Hepatic protein and nucleic acid content in Dipsosaurus dorsalis following hypophysectomy and treatment with estradiol-17β and growth hormone

Abstract 1. 1. Estradiol-17β treatment to female lizards, Dipsosaurus dorsalis , produced enlarged livers with markedly elevated protein/DNA and RNA/DNA. 2. 2. Quantitatively similar changes in these parameters were obtained in hypophysectomized animals when growth hormone was administered in addition to estrogen, but not when either hormone was given singly. 3. 3. Growth hormone was required to evoke an elevation in total plasma protein level in hypophysectomized lizards treated with the estrogen of a similar magnitude to that obtained by estrogen treatment to the intact animals. 4. 4. These results indicate that estrogen-induced vitellogenesis requires the mediation of the pituitary.

The influence of intrahypothalamic implants of progesterone on ovarian growth and function in the ovoviviparous iguanid lizard, Sceloporus cyanogenys

Abstract 1. 1. Implants of progesterone were made in the brain, pituitary and subcutaneous locations in lizards (Sceloporus cyanogenys) during the phase of ovarian growth. 2. 2. Implants located in the hypothalamus were very effective in preventing futher ovarian development, an action that mimicked that of hypophysectomy. 3. 3. Implants in other regions of the brain, in the pituitary or subcutaneous locations were ineffective in preventing ovarian growth and subsequent ovulation. 4. 4. Plasma progesterone titers were not increased by progesterone implants.

The effect of hypothalamic lesions and hypophysectomy on adrenal weight in Sceloporus cyanogenys

Abstract Adrenal hypertrophy was induced in male Sceloporus cyanogenys with Metyrapone. Radiofrequency lesions of the anteromedial hypothalamus and of the median eminence were followed by a decrease in the weights of the adrenal glands compared to those of the control animals, and hypertrophy of the glands did not occur following metyrapone. Both sham-operation and lesions of other areas of the brain (cerebral hemisphere, posterior and lateral hypothalamus) increased adrenal weight; however, the weight increase induced by sham-operation was less than that induced by lesions of these areas of the brain. While Metyrapone increased adrenal weight in all groups other than those with lesions of the anteromedial hypothalamus and median eminence, the increase over and above that caused by the lesions of other areas of the brain was not statistically significant. Lesions of the hypothalamus, wherever placed, increased thyroid weight whereas lesions of the cerebral hemispheres did not. Hypophysectomy prevented the adrenal weight response to Metyrapone, and the injection of ACTH increased adrenal weight in both intact and hypophysectomized animals.