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PubMed1985

Thyroid function in adult rough-skinned newts (Taricha granulosa): effects of hypophysectomy and hormone replacement.

This study examines the regulation of thyroid activity in adult rough-skinned newts, Taricha granulosa. Aquatic, breeding-condition newts were hypophysectomized and were injected for 23 days with the mammalian adenohypophysial hormones: ACTH, PRL, and GH. During a fourth week of treatment, these newts also received TSH. Plasma T4 concentrations were lower in hypophysectomized newts than in sham-hypophysectomized newts 23 days after surgery. Both ACTH and PRL increased T4 titers above these in saline-injected control newts; GH alone had no effect. TSH effectively increased the plasma T4 concentrations in newts from all five groups. GH, and possibly PRL, depressed the response to TSH. Plasma T4 concentration was positively correlated with body fluid loss, suggesting that hormone concentration/dilution effects may occur generally in animals such as these that undergo substantial seasonal changes in degree of hydration.

Adrenocorticotropic Hormone↗
PubMed1987

Effect of gonadectomy and hypophysectomy on plasma steroid levels in male and female lampreys (Lampetra fluviatilis, L.).

Testosterone, estradiol, and dehydroepiandrosterone (T, E2, and DHA) were measured by RIA in plasma samples from three groups of sexually immature male and female (male, female) river lampreys: (I) intact, (II) gonadectomized, or (III) with pro- and mesoadenohypophysis removed (hypophysectomized). T levels were around 0.1 ng/ml in both I male and I female and increased significantly in all operated groups, especially in II male, to 1.2 ng/ml. E2 levels were between 0.7 and 1 ng/ml in I male and I female and were significantly elevated only in II male to 2.0 ng/ml. DHA levels showed significant decreases, from around 0.9 ng/ml in I male and I female, in both operated groups. It is suggested that T and E2 are secreted from a nongonadal source in both sexes and then converted to biologically active sex hormones in the gonads. Therefore T and E2 do not decrease, and may even accumulate, in the blood after gonadectomy. Since extirpation of the pro- and mesoadenohypophysis was not followed by a decrease in T and E2, their secretion may be stimulated by a hormone from another part of the pituitary such as the metaadenohypophysis.

Animals↗
PubMed1989

Effects of hypophysectomy and ovariectomy on hepatic estrogen receptor content in the turtle, Chrysemys picta.

Estrogen receptor (ER) content in the cytosol and nuclear extract of the liver of adult female Chrysemys picta (control females) was measured in February, May, early June, and late June. Both cytosolic (C) and nuclear (N) hepatic ER content rose from low levels (C: 189 +/- 19; N: 52 +/- 23 fmol/g tissue) in February to significantly higher levels in May (C: 437 +/- 15; N: 124 +/- 25 fmol/g tissue) before declining to lower values in early June (C: 298 +/- 19; N: 118 +/- 20 fmol/g tissue) and late June (C: 274 +/- 22; N: 89 +/- 13 fmol/g tissue). This pattern of seasonal variation in hepatic ER content was also observed in gonadectomized females. Levels of hepatic ER content in ovariectomized turtles fluctuated in the same manner as those found in control females. However, elevations in hepatic ER contents were not observed in hypophysectomized females. Removal of the pituitary resulted in a drastic reduction in the May value (316 +/- 49 fmol/g tissue) of cytosolic ER content and a complete blockade in a rise of nuclear ER content in the liver of the turtle. Nuclear hepatic ER content remained at around 50 fmol/g tissue throughout the months of May and June. The two surgeries procedures caused no significant changes in the ER's affinity for estrogen. The present findings demonstrate a direct control of the pituitary over hepatic ER content which signifies important pituitary regulation of the vitellogenic process, at the liver level, during the spring reproductive season.

Animals↗