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Biomedical subjects

S A Sower

Publications and source records attributed to S A Sower.

At least 55 records · Page 3Linked to original sources
PubMed1992

Changes in plasma thyroxine, estradiol-17 beta, and 17 alpha,20 beta-dihydroxy-4-pregnen-3-one during smoltification of coho salmon.

Circulating levels of plasma estradiol, 17 alpha,20 beta-dihydroxy-4-pregnen-3-one (17 alpha,20 beta PROG), and thyroxine were measured during smoltification of coho salmon in two successive years (1984 and 1985). Two elevations of thyroxine occurred in both years, the first occurred in April followed by a second increase in May. Estradiol levels were dynamic with variable changes particularly in postsmolts when estradiol levels were either depressed in 1984 or high in 1985. However, elevations of estradiol preceded the second elevation of thyroxine in May in both years when the salmon were undergoing the later stages of smoltification. There were no consistent changes of plasma 17 alpha,20B PROG during this period. Although, in 1984, there were significant elevations and depressions of 17 alpha,20B PROG, and in 1985, there was a major unexplained depression of 17 alpha,20B PROG on April 24. There were no sexual differences noted for plasma steroid levels in the juvenile fish. These data suggest that there are seasonal changes of estradiol coinciding with other developmental changes during smoltification.

Animals↗
PubMed1992

Sex steroid levels in the testes, ovaries, and pyloric caeca during gametogenesis in the sea star Asterias vulgaris.

The concentrations of progesterone, testosterone, and estradiol were determined via radioimmunoassay in testes, ovaries, and pyloric caeca of the sea star Asterias vulgaris during one complete and two partial gametogenic cycles. These compounds were found in all tissues examined and were present in quantities similar to those reported previously in other echinoderms and in vertebrates. Testes and ovaries exhibited annual growth cycles during which testicular and ovarian mass increased up to 100-fold as gametes were produced and stored until spawning. Pyloric caecal mass varied during the annual reproductive season; however, no seasonal trends were apparent. In the testes, sex steroid levels were highest at the onset of spermatogenesis. Transient increases in the levels of estradiol coincided with spermatogonial mitotic proliferation. Transient increases in the levels of testosterone and progesterone in the testes coincided with spermatogenic column formation and with spermiogenesis, respectively. In the ovaries, estradiol and testosterone levels were highest at the onset of oogenesis while progesterone levels did not change significantly throughout the annual gametogenic cycle. Male and female pyloric caeca exhibited similar seasonal variations in levels of sex steroids as compared with the gonads. It is hypothesized that transient increases in the levels of sex steroids during gametogenesis may serve as endogenous modulators of reproduction.

Animals↗
PubMed1992

Changes in brain gonadotropin-releasing hormone, pituitary and plasma gonadotropins, and plasma thyroxine during smoltification in chinook salmon (Oncorhynchus tschawytscha).

Concentrations of brain salmon gonadotropin-releasing hormone (sGnRH), plasma gonadotropin I (GTH I), and pituitary GTH I and GTH II were determined in yearling chinook salmon (Oncorhynchus tschawytscha) during the parr-smolt transformation in two successive seasons. There were significant elevations in brain sGnRH content from February to March in 1988, and from February to April in 1989. Increases in brain sGnRH content coincided with elevations in plasma thyroxine levels that occurred from February to March, 1988 and 1989. Plasma GTH levels were relatively constant (1-2 ng/ml) throughout the period of sampling. However, during 1988, plasma concentrations of GTH I decreased significantly between late March and early April. During 1989, plasma GTH I levels appeared to reach a peak (2 ng/ml) in mid-February, but otherwise remained near 1 ng/ml. Previous studies have shown that GTH II was not detectable in plasma at this stage. During 1989, pituitary GTH I concentrations were 50- to 70-fold higher than that of GTH II, and increased, though not significantly, from February through April. Although GTH II was detected in the pituitary by RIA, it is likely that the measurable levels are due to GTH I cross-reaction in the GTH II RIA. Histological examination of the gonads indicated that throughout smoltification the oocytes remained in the perinucleolar stage of oogenesis and the testes were in the spermatogonial stage of spermatogenesis. Although no observable changes in gametogenesis occurred, the changes in brain sGnRH content, plasma GTH I levels, and pituitary GTH content suggest that some changes in the hypothalamic-pituitary axis may occur during smoltification.

Animals↗
PubMed1992

Estrogen- and progesterone-dependent secretory changes in the uterus of the sheep.

This study was undertaken to determine the effects of 17 beta-estradiol (E) and progesterone (P) on polypeptide synthesis and release from the uterus of the sheep. Uterine flushings (UF) and endometrium were obtained from ovariectomized untreated animals, ovariectomized animals treated with E (approximately 5-10 pg/ml) for 6 days (6E) and ovariectomized animals primed with E for 6 days then treated with P (approximately 1.5-3 ng/ml), in the continued presence of E, for an additional 6 days (6EP). Endometrium was cultured (24 h) in the presence of 3H-leucine (3H-leu) or 3H-glucosamine (3H-glcN), and newly synthesized and released proteins were detected in culture media by fluorography of 10% SDS gels. The quantity of proteins in UF and radiolabeled proteins in explant culture media did not change between treatment groups (p < 0.05). Qualitative changes in the synthesis and release of proteins were observed depending on the steroid treatment. An M(r) 57,000 protein was present in UF and 3H-leu-labeled culture media obtained from animals treated only with E and an M(r) > 200,000 was present in 3H-leu-labeled culture media of endometrium obtained from 6E and 6EP animals. An M(r) 44,000 protein was present only in UF from 6EP animals but could not be detected in endometrial culture media from animals undergoing this steroid treatment. These data show that the endometrium of the ovariectomized sheep undergoes alterations in secretory protein patterns which depend on the presence of E and P.

Animals↗
PubMed1991

Plasma estradiol and progesterone after hypophysectomy and substitution with pituitary in female sea lampreys (Petromyzon marinus).

This study investigated plasma steroid concentrations 1 week after total hypophysectomy in adult female sea lampreys. Plasma estradiol significantly decreased (to 1.19 +/- 0.17 SE ng/ml) following hypophysectomy and was elevated (to 1.91 +/- 0.11 ng/ml) to a value similar to controls by a single injection of two pituitary equivalents in adult female sea lampreys in the stage of final maturation. Plasma progesterone also significantly decreased (to 69 +/- 10 pg/ml) following hypophysectomy and was elevated (to 183 +/- 71 pg/ml) to a value not different from uninjected controls by a single injection of two pituitary equivalents in females. Injection of two pituitary equivalents did not affect plasma estradiol in intact lampreys but surprisingly decreased plasma progesterone (to 67 +/- 14 pg/ml) compared to saline-injected intact lampreys (318 +/- 142 pg/ml). The decrease in estradiol and progesterone after hypophysectomy and their normalization after injection of pituitaries support the concept that the secretion of estradiol and progesterone is stimulated by gonadotropin or other pituitary hormones.

Animals↗
PubMed1990

Relationship between brain gonadotropin-releasing hormone and final reproductive period of the adult male sea lamprey, Petromyzon marinus.

Gonadotropin-releasing hormone (GnRH) concentrations were measured in brains of adult male sea lamprey, Petromyzon marinus, during their final reproductive period. The lampreys were collected during their upstream migration in coastal New Hampshire rivers and sampled at the trap (referred to as Group A) or they were transferred to an artificial spawning channel (referred to as Group B). Plasma estradiol and progesterone were also measured, and histological examination of the gonadal stages was done as well. The concentrations of brain GnRH and plasma estradiol fluctuated significantly through time. There was a rise in brain concentrations of GnRH coincident with an increase in temperature just prior to spawning. In addition, there was a significant progressive correlation between increasing plasma estradiol and temperature in lampreys from Group B during the period studied. These studies provide evidence for progressive seasonal relationships between changes in brain GnRH and gametogenic and steroidogenic activity of the gonads in adult male sea lampreys during their final reproductive period.

Amino Acid Sequence↗
PubMed1988

Neuronal systems immunoreactive with antiserum to lamprey gonadotropin-releasing hormone in the brain of Petromyzon marinus.

The role of gonadotropin-releasing hormone (GnRH) in mammalian reproduction has been studied extensively; however, the role of a structurally different, but related, decapeptide is not well characterized in the most primitive class of vertebrates, Agnatha. Utilizing an antiserum directed to the recently characterized lamprey GnRH, we examined immunoreactive neuronal perikarya and nerve fibers in sections from the brain of the sea lamprey, Petromyzon marinus, using the unlabeled peroxidase-antiperoxidase method. Neuronal perikarya and fibers were immunopositive with antisera generated to lamprey GnRH and also to certain antisera generated to mammalian GnRH. Immunopositive neuronal perikarya were detected in an arc-shaped population extending from ventral to dorsal preoptic areas. Fibers from these cells projected to the neurohypophysis via the preoptico-hypophyseal tract, but in addition also protruded into the third ventricle. Additionally, some fibers coursed along the external surface of the brain, and may also release GnRH into meningeal compartments. The presence of fully processed, mature decapeptide is indicated within neuronal perikarya, as well as in projecting nerve fibers and terminals. No reaction product was detected in sections incubated with an antiserum to the interior amino acid sequences of mammalian LHRH. This finding supports the structure reported for lamprey GnRH by Sherwood et al. (1986).

Animals↗
PubMed1988

Arginine vasotocin from the pituitary gland of the lamprey (Petromyzon marinus): isolation and amino acid sequence.

Arginine vasotocin (AVT) was isolated from extracts of sea lamprey pituitary glands (Petromyzon marinus). The amino acid sequence Cys-Tyr-Ile-Gln-Asn-Cys-Pro-Arg-Gly-NH2 is identical to the molecule isolated from teleosts and tetrapods. The total yield was estimated to be 9.6 pmol per gland. No evidence could be found for the existence of a second neurohypophyseal nonapeptide in the lamprey pituitary.

Amino Acid Sequence↗
PubMed1987

Endocrine events associated with spawning behavior in the sea lamprey (Petromyzon marinus).

Levels of estradiol, progesterone, and testosterone were determined in plasma of sea lamprey (Petromyzon marinus) undergoing certain behaviors associated with spawning in natural and artificial stream environments. Significantly higher levels of estradiol, progesterone, and testosterone were found in males than in females. In the artificial spawning channel, levels of estradiol were significantly higher in females exhibiting resting and swimming behaviors than in fanning, nest building, and spawning behaviors. No significant correlation was found with either progesterone or testosterone levels and the various reproductive behaviors. The data presented are the first experimental evidence that suggest gonadal steroids may be correlated with certain reproductive behaviors in the sea lamprey.

Aggression↗
PubMed1987

Comparative biological properties of lamprey gonadotropin-releasing hormone in vertebrates.

The biological activities of lamprey GnRH were determined in the lamprey, chicken, sheep, and rat. Lamprey GnRH elevated plasma steroid levels and stimulated ovulation in the lamprey, but had little or no LH-releasing activity in chicken and sheep pituitary bioassays or effect on GnRH receptor-binding activity in the rat pituitary. The lamprey GnRH molecule is structurally distinct from other known vertebrate GnRHs and is the first identified molecule in this family to have different amino acids in the third and sixth positions. These data suggest that the presence of Tyr3 or Glu6 in lamprey GnRH may account for the lack of biological activity in the representatives of the two different vertebrate classes investigated in this study.

Animals↗
PubMed1986

Primary structure of gonadotropin-releasing hormone from lamprey brain.

The primary structure of gonadotropin-releasing hormone (GnRH) isolated from whole brains of lamprey is pGlu-His-Tyr-Ser-Leu-Glu-Trp-Lys-Pro-Gly-NH2. This unique decapeptide was isolated and purified from brain extracts by reverse-phase high performance liquid chromatography. The structure of the peptide was established from chymotryptic fragments that were identified by protein sequence analysis and fast atom bombardment mass spectrometry. The peptide reacts with an antiserum raised against mammalian GnRH and is structurally identified as a member of the GnRH family by the amino and carboxyl termini of pGlu1-His2 and Pro9-Gly10NH2, the conservation of Ser4 in the internal segment of the molecule and its length of 10 amino acids. For the first time, amino acid substitutions are found in positions 3 and 6, critical for biological potency and conformation, respectively. Additionally, a second form of GnRH (lamprey II GnRH), representing about 10% of the total GnRH immunoreactive material in the brain, was isolated; its amino acid composition differs by 3 residues from lamprey I GnRH. Synthetic lamprey I GnRH elevates plasma estradiol in adult female lampreys.

Amino Acid Sequence↗
PubMed1985

Steroid and thyroid hormone profiles following a single injection of partly purified salmon gonadotropin or GnRH analogues in male and female sea lamprey.

The effects of exogenous administration of gonadotropin-releasing hormone (GnRH) analogues or of a partly purified salmon gonadotropin extract (GTH) on the duration of steroid and thyroid hormone levels were determined in female and male sea lampreys, Petromyzon marinus, tested under differing temperature and reproductive status. Plasma estradiol levels, but not androgens, were significantly elevated in response to the GnRH analogues or GTH injection compared to controls in female and male lampreys. Higher temperature and/or advance in time of maturation appeared to be inversely related to plasma estradiol levels. These data provide further evidence of hypothalamic control over reproductive function in lampreys. Plasma thyroxine was significantly elevated after female lampreys were treated with GTH, GnRHa (10 micrograms/lamprey) or GnRHa (1 microgram/lamprey) compared to controls. The present study is the first to demonstrate that the GnRH analogue stimulated in some way the pituitary-thyroid axis. These data suggest that a GnRH activity may activate both gonado- and thyrotropic secretion or that the endogenous hormone may itself have both functions in one of the most primitive vertebrates, the sea lamprey.

Animals↗
PubMed1985

Corticotrophin-like bioactivity in the pituitary gland and brain of the pacific hagfish, Eptatretus stouti.

The cytochemical bioassay for corticotrophin (ACTH) was used in an attempt to detect ACTH-like activity in the Pacific hagfish, Eptatretus stouti. Extracts of the pituitary gland and brain were active in this assay system but those of liver and skeletal muscles were not. The slopes of the dose-response lines of the pituitary extracts were less than those of the mammalian corticotrophin standard preparation but greater than those of the brain extracts. The results suggest that the corticotrophic factor in the hagfish differs from mammalian ACTH.

Adrenal Glands↗
PubMed1985

Changes in plasma steroid and thyroid hormones and insulin during final maturation and spawning of the sea lamprey, Petromyzon marinus.

Circulating levels of plasma estradiol-17 beta, androgens, thyroxine, triiodothyronine, immunoreactive insulin, plasma fatty acids, and protein were measured at interval during the period of final gonadal maturation, prior to spawning of male and female sea lampreys. Plasma estradiol levels fluctuated significantly and generally covaried in males and females through time. In females, possibly in relation to environmental changes, mean plasma estradiol levels peaked four times during the final spawning period but decreased sharply at the time of ovulation. In males, mean plasma estradiol peaked seven times during the final prespawning period and, in contrast to females, peaked significantly at the time of final spermiation. Plasma androgens were extremely low and covaried in males and females through time. Like plasma steroid profiles, there were coordinated changes in plasma triiodothyronine and thyroxine levels in males and females through the prespawning season. There was a slight increase in plasma insulin during the terminal maturation of the lampreys. However, at ovulation, the insulin levels abruptly decreased in females, whereas in males they remained unchanged. Plasma protein and fatty acid levels gradually decreased until ovulation/spermiation. At ovulation plasma fatty acid levels increased.

Androgens↗
PubMed1985

A new family member for gonadotropin-releasing hormone.

The two living representatives of the most ancient vertebrates, Agnathans, are lamprey and hagfish. Using immunological methods, we identified gonadotropin-releasing hormone (GnRH)-like molecules in the lamprey brain, but not hagfish. The lamprey GnRH was detected poorly by antisera directed at the C-terminus, suggesting that a C-terminal amino acid substitution may have occurred in the lamprey molecule compared with mammalian GnRH. In spite of this, lamprey and mammalian GnRH-like molecules have the same retention time on an isocratic HPLC system and parallel inhibition of mammalian 125I-GnRH in a radioimmunoassay. The lamprey GnRH-like molecule has a distinct HPLC elution pattern compared with dogfish shark, salmon, trout and probably birds. Thus lamprey GnRH represents another member of the growing family of GnRH molecules. Additionally, lamprey GnRH may be a stem molecule in the vertebrate evolution of GnRH.

Animals↗
PubMed1984

Changes in plasma estradiol and effects of triiodothyronine on plasma estradiol during smoltification of coho salmon, Oncorhynchus kisutch.

Plasma estradiol-17 beta levels were measured by radioimmunoassay in untreated coho salmon of both sexes or in fish fed triiodo-L-thyronine during the smoltification period. Mean plasma estradiol increased between February 25 and April 1 from 94 to 142 pg/ml, and then by May 13, it had decreased to 80 pg/ml. This hormonal cycle was followed by a second significant increase to 219 pg/ml on June 22. Plasma thyroxine level covaried with that of estradiol. Treatment with triiodothyronine had no effect on plasma estradiol or thyroxine levels. Plasma estradiol surges during the smoltification period must be considered along with other significant endocrine changes for a possible role in the developmental phenomena that characterize this period.

Animals↗
PubMed1983

The effect of insulin insufficiency on plasma thyroid hormones and some metabolic constituents in Pacific hagfish, Eptatretus stouti.

The effect of guinea pig anti-human insulin serum was studied in Pacific hagfish. The metabolic indicators of insulin insufficiency, such as elevation of plasma glucose, free fatty acids, and alpha-amino nitrogen levels were obtained at 72 and 120 hr after anti-insulin serum injection. Plasma triiodothyronine levels declined significantly 24 hr after anti-insulin serum administration. These findings supplement earlier data with the same species and suggest that the regulatory metabolic action of insulin and thyroid hormones are related in cyclostomes.

Animals↗