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I P Callard

Publications and source records attributed to I P Callard.

At least 37 records · Page 2Linked to original sources
PubMed1990

Vertebrate vitellogenesis: molecular model for multihormonal control of gene regulation.

The stimulation of yolk protein synthesis by estrogen is a characteristic of female non-mammalian vertebrates; in mammals, however, vitellogenesis has been suppressed as a corollary of the evolution of viviparity. It is our hypothesis that progesterone has a dual role in this phylogenetic trend; a) to inhibit myometrial contraction and thus set the stage for internal development of embryos and associated placentation, b) to inhibit yolk protein synthesis as placentation became an efficient direct supply of nutrients to the fetus. We have presented evidence that in the reptiles, the central vertebrate group from which the ancestors of modern mammals evolved, the control of yolk protein synthesis is complex, involving both pituitary and ovarian steroids (estradiol, testosterone and progesterone). This system provides an excellent model for the multihormonal contents of gene regulation involving both + and - controls.

Animals↗
PubMed1989

Two progesterone receptors in the oviduct of the freshwater turtle Chrysemys picta: possible homology to mammalian and avian progesterone receptor systems.

Two progesterone receptors in the oviduct of the freshwater turtle Chrysemys picta: possible homology to mammalian and avian receptor systems. Here we report the characterization of two specific progesterone receptors in nuclear extracts of the turtle oviduct. The receptors differ in dissociation constants (2.8 nM vs 27 nM) which can be separated on DEAE-Sepharose, the former eluting at 0.08 M KCl and the latter at 0.20 M KCl. [3H]R5020 photoaffinity labeling SDS-PAGE revealed that the 2.8 nM moiety migrates with an apparent molecular weight of 80 +/- 5 kDa and the 27 nM moiety migrates with an apparent molecular weight of 120 +/- 5 kDa. These receptors are termed PR-A and PR-B due to their molecular mass and elution profiles. DNA-cellulose chromatographic studies show that both bind DNA-cellulose with the PR-A eluting at 0.09 M NaCl and PR-B eluting between 0.20-0.21 M NaCl. In reproductively inactive turtles (from the months of January and February) estradiol is undetectable, and PR-B is absent as determined by Scatchard analysis, [3H]R5020 photoaffinity labeling electrophoretic studies and DEAE-Sepharose and DNA-cellulose chromatography. In these animals PR-B can be replenished by estrogen treatment, suggesting a physiological role for both PR-A and PR-B and dependence of PR-B on estradiol.

Animals↗
PubMed1988

Changes in pituitary responsiveness during the ovulatory cycle of the Japanese quail, in vitro.

Anterior pituitary glands from ovulating Japanese quail (Coturnix coturnix) were used to investigate variation in sensitivity to chicken luteinizing hormone-releasing hormone (cLHRH I; Gln8-LHRH). Grouping the pituitaries by ovulatory stage provided preliminary evidence of changes in sensitivity to LHRH during the ovulatory cycle. Pituitaries taken from quail before the preovulatory LH surge were responsive to cLHRH I, while pituitaries from the other times of the cycle showed minimal response to cLHRH I. Female pituitary glands release less LH than those of males. These data indicate a change in sensitivity to LHRH in the female quail that may be due to changes in gonadal steroids or the pool of releaseable LH from the pituitary.

Animals↗
PubMed1988

In vivo steroidogenic effects of homologous pituitary ventral lobe extract in the spiny dogfish, Squalus acanthias.

Pregnant Squalus acanthias were injected intravenously with aqueous extract equivalent to three pituitary ventral lobes (VL). Blood samples were withdrawn by caudal sinus puncture at intervals over a period of 72 hr and plasma progesterone, testosterone, and estradiol-17 beta measured by radioimmunoassay. Early pregnancy animals (Stage A) failed to respond, but mid-pregnancy animals (Stage C) responded to VL with significant increases in plasma steroids. Plasma progesterone and testosterone were increased sevenfold and plasma estradiol-17 beta fourfold by 10-24 hr postinjection. These studies demonstrate pregnancy stage-dependent differences in gonadal sensitivity to a pituitary ventral lobe gonadotropic moiety.

Animals↗
PubMed1988

Seasonal variations in oviductal activity, extensibility, and tensile strength in Chrysemys picta.

In vivo and in vitro myometrial activity, tissue extensibility, and tensile strength were measured during the annual cycle of the female turtle Chrysemys picta. Contractile rate, in vivo and in vitro, increased to a maximum in the periovulatory period, but contractile strength in vitro was inversely proportional to rate, being least in the periovulatory period. Initial oviductal circumference was highest in April and lowest in September. Although extensibility varied little, this parameter was inversely proportional to the initial circumference. Tensile strength was greatest in midwinter and least in postovulatory animals. The results are discussed in relationship to the known seasonal endocrine cycle and suggest important hormonal (estrogen, progesterone) effects upon egg retention and egg laying in this species.

Animals↗
PubMed1988

The annual testicular cycle in the turtle, Chrysemys picta: a histochemical and electron microscopic study.

This work is a study of testicular function in Chrysemys picta using changes in ultrastructure and steroid histochemistry as indices of Leydig and Sertoli cell activity. The cytological features of these cells are described in reference to four periods of tubular development. Leydig and Sertoli cells show distinct changes in morphological appearance during the seasonal cycle. Leydig cells are hypertrophic with an active 3 beta-hydroxysteroid dehydrogenase (HSD) and abundant smooth endoplasmic reticulum (SER) in early spring when androgen levels are high and animals mate and atropic in mid-summer when spermatogenesis is proceeding. Leydig cell atrophy is associated with a reduction in the volume of cytoplasm and SER. Leydig cells become active again in the fall showing a return toward the spring condition, with an increase in 3 beta-HSD activity. In contrast, although Sertoli cells show variations in abundance of organelles and inclusions during the annual cycle, no obvious degenerative changes could be seen and SER is always present. 3 beta-HSD enzyme activity in Sertoli cells is weak or absent in spring but intense during summer. Taken together, these observations suggest that Sertoli and Leydig cell functions are asynchronous.

Animals↗
PubMed1988

A plasma steroid hormone binding protein in the viviparous water snake, Nerodia.

A plasma steroid binding protein (SHBP) with medium-high affinity and limited capacity was characterized in the viviparous water snake, Nerodia. This SHBP shows similarity to SHBPs previously described in some other nonmammalian species. A single binding component was detected by Scatchard analyses with a medium-high affinity for testosterone (T), estradiol (E), progesterone (P), and corticosterone (B). Equilibrium dissociation constants (Kd) for these steroids are as follows: T, 3.6 x 10(-8) M; E, 3.7 x 10(-8) M; P, 5.9 x 10(-8) M; B, 12.1 x 10(-8) M. In competition studies (at saturation) the relative binding affinities (RBA) for E (1.0) and T (1.0) were higher than those for P (0.8) and B (0.59). Further analysis of binding specificity for [3H]estradiol at 100-fold excess competitor concentrations revealed that dihydrotestosterone also competes; however, estrone and estriol were relatively poor competitors. Displacement of 3H-E by antiestrogen clomiphene derivatives and synthetic estrogen varied; enclomiphene citrate (67.8%), clomiphene citrate (42.2%), diethylstilbestrol (37.3%), and zuclomiphene citrate (15.2%). The SHBP has a relatively high binding capacity (Bmax = 0.09-0.7 M), which may be correlated with the relatively high circulating plasma steriod levels in this species. Scatchard analysis, disc gel electrophoresis, sucrose gradient centrifugation, and competition studies indicate the presence of a single moiety binding estradiol, testosterone, progesterone, and corticosterone. The estradiol-SHBP complex is unstable, exhibiting very short times of association (t less than 1.5 min) and dissociation (Kd = 0.0165 sec-1, t 1/2 = 18.3 sec). Measurement of SHBP levels throughout the seasonal reproductive cycle revealed high levels of binding in previtellogenic, vitellogenic, early pregnant, and postpartum animals. A significantly lower level of SHBP was detected in mid-late pregnancy.

Animals↗
PubMed1988

Hepatic progesterone receptors: characterization in the turtle Chrysemys picta.

High and low affinity progesterone (P)-binding proteins similar to those described in the chick oviduct were characterized for the first time in liver cytosol in an oviparous turtle, Chrysemys picta. Two forms of high affinity P receptor were separated by diethyl aminoethyl (DEAE)-Sepharose anion exchange chromatography; the A form eluted in low salt buffer, and the B form at a KCl concentration of 0.20 M in a linear gradient. After photoaffinity labeling of crude cytosol with [3H] R5020, two overlapping peaks of radioactivity were detected with sodium dodecyl sulfate-polyacrylamide gel electrophoresis. After separation with DEAE-Sepharose and photoaffinity labeling, the A form migrated as a single peak with a mol wt of 90,000, and the B form as a single peak with a mol wt of 123,000. The affinity (Kd, 2.9 X 10(-9) M), capacity (1 pmol/mg protein), and binding specificity were characteristic of a P receptor. P competed most effectively for [3H]P binding. R5020 and deoxycorticosterone were good competitors; 5 alpha-pregnenolone, 17 alpha-hydroxyprogesterone, and testosterone were quite effective; cortisol, corticosterone, aldosterone, and 5 alpha-dihydrotestosterone were poor competitors. A lower affinity P-binding component (Kd, 1 X 10(-7) M; maximum binding, 15 pmol/mg protein) co-eluted from DEAE-Sepharose columns with the A and B receptor forms. This is the first description of a hepatic P receptor in any vertebrate.

Affinity Labels↗
PubMed1988

An estrogen receptor in the liver of the viviparous watersnake, Nerodia; characterization and seasonal changes in binding capacity.

Understanding of steroid receptors is derived largely from the mammalian uterus and avian oviduct, and we have sought to characterize steroid receptors in relationship to natural cycles in subavian species. Here we report a putative estrogen receptor associated with the vitellogenic cycle in the female viviparous watersnake, Nerodia. Estrogen binding in cytosolic and nuclear hepatic cell extracts exhibits the following characteristics: high affinity (Kd, 1.3 X 10(-9) M cytosol; 5.7 X 10(-10) M nuclear extract), steroid specificity for natural estrogens, association time of 1 h at 22 C and 4 h at 0 C, and dissociation rate of 0.0268 min-1 at 0 C (half-time, 11.2 min) and 0.322 min-1 at 22 C (half-time, 0.906 min). Both cytosolic and nuclear estrogen binding are target organ specific; binding is low to undetectable in lung, skeletal muscle, and intestine and present in liver, oviduct, and kidney. A sedimentation coefficient of 6S was demonstrated in cytosol under low or high salt conditions, and a sedimentation coefficient of 3.5S was found in nuclear extract. Nuclear location of the receptor is indicated by extraction of increasing amounts of receptor by increasing KCl concentrations up to 0.5 M; 50% of the binding is extracted by 0.16 M KCl. Nuclear estrogen binding is increased significantly after estrogen injection. This estrogen-binding moiety is unusual, since it does not bind to the synthetic estrogen diethylstilbestrol, to antiestrogen clomiphene derivatives, or to calf thymus DNA-cellulose and diethylaminoethyl-Sepharose. Significant changes in cytosolic and nuclear hepatic estrogen receptor levels correlate with vitellogenic stage.

Animals↗
PubMed1987

Relaxin from an oviparous species, the skate (Raja erinacea).

An acid-acetone extract prepared from ovaries of the skate, Raja erinacea, contained a weakly crossreacting molecule when tested in a pig relaxin radioimmunoassay. The material was isolated and purified to homogeneity by ion exchange chromatography, molecular exclusion chromatography, and HPLC. Analytical tests proved the molecule to consist of two chains and to have a molecular weight of 7,500. Sequence analyses of the A and B chains yielded the following sequence: Glu-Glu-Lys-Met-Gly-Phe-Ala-Lys-Lys-Cys-Cys-Ala-Ile-Gly-Cys-Ser-Thr-Glu- Asp-Phe-Arg-Met-Val-Cys and Arg-Pro-Asn-Trp-Glu-Glu-Arg-Ser-Arg-Leu-Cys-Gly-Arg-Asp-Leu-Ile-Arg-Ala- Phe- Ile-Tyr-Leu-Cys-Gly-Gly-Thr-Arg-Trp-Thr-Arg-Leu-Pro-Asn-Phe-Gly-Asn-Tyr- Pro-Ile-Met respectively. Skate relaxin has 0.2% of the activity of B29 pig relaxin in the symphysis pubis assay and 0.5% in the mouse uterine muscle strip contraction inhibition assay.

Amino Acid Sequence↗
PubMed1987

Steroids modulate the release of luteinizing hormone from quail pituitary cells.

An enzymatically dispersed pituitary preparation from male Japanese quail (Coturnix coturnix) was used to study the effects of gonadal and adrenal steroids on gonadotropin release. Cells were preincubated for 18 hr with or without steroids and then challenged with chicken luteinizing hormone-releasing hormone (cLH-RH I; Gln8-LH-RH). Preincubation with testosterone (T; 10 nM) significantly suppressed (P less than 0.05) luteinizing hormone release in response to cLH-RH I (10 ng/ml). Preincubation with 5 alpha-dihydrotestosterone (5 alpha-DHT) (10 nM) caused even further suppression of LH-RH-stimulated LH release while the same concentration of 5 beta-dihydrotestosterone and estradiol-17 beta had no effect. In addition, preincubation with corticosterone (10 nM) significantly (P less than 0.01) suppressed the amount of LH released in response to cLH-RH I. Pituitary cells from immature males, when stimulated with cLH-RH I, released LH in a dose-related manner. Neither T nor 5 alpha-DHT (10 nM) altered the effect of LH-RH. These data suggest that T and 5 alpha-DHT play a role in mediating LH release in the avian pituitary while 5 beta-reduced androgens have no effect. There appears to be no androgen effect in the immature quail. In addition, corticosterone seems to be a factor in controlling gonadotropin secretion in the quail.

Animals↗
PubMed1987

Morphological and endocrine correlates of the reproductive cycle of the aplacental viviparous dogfish, Squalus acanthias.

Pregnant female spiny dogfish were captured off the coasts of Maine and Massachusetts and morphometric and gravimetric analyses of the liver, gonad, and reproductive tract correlated with the reproductive cycle. Plasma samples were taken and circulating steroids (progesterone, testosterone, and estradiol) were measured by radioimmunoassay. Clear-cut temporal variations in plasma steroid levels were observed, which correlated with the ovarian cycle. Testosterone and estradiol-17 beta levels were low (100-200 pg/ml plasma) in early pregnancy when ovarian follicles were small but increased to about 10 ng/ml as follicles grew and gestation progressed. By contrast, plasma progesterone was high (2-6 ng/ml) in early to mid-pregnancy when corpora lutea were active and declined toward term (less than 1.0 ng/ml).

Animals↗
PubMed1987

Hepatic estrogen receptor in the turtle, Chrysemys picta: partial characterization, seasonal changes and pituitary dependence.

A hepatic estrogen receptor is described from female turtles, Chrysemys picta. The receptor adheres to DNA after incubation with [3H]estradiol and can be eluted with a linear salt gradient as a single component with an elution maximum of 0.21 M. It is steroid-specific, binding estrogens, but not androgens or progestins. Specific binding saturates between 3 and 7 nM [3H]estradiol-17 beta and Scatchard analysis gave a Kd of 2 X 10(-9) M and a maximal binding capacity of 3.02 fmol/mg protein. Hypophysectomy reduces hepatic estradiol receptor from 70 fmol/g tissue in control animals to non-detectable levels. Growth hormone replacement partially restored the receptor to 36% of control. Significant changes in receptor occur during the ovarian cycle.

Animals↗
PubMed1987

Luteinizing hormone secretion from the quail pituitary in vitro.

An enzymatically dispersed pituitary preparation from Japanese quail (Coturnix coturnix) was used to study the dynamics of gonadotropin release. After an 18-h incubation, the cells were challenged with different luteinizing hormone-releasing hormones (LHRH) for 90 min. Using pituitary cells from mature males, mammalian and chicken LHRH I (Gln8-LHRH) had approximately equal luteinizing hormone (LH)-releasing activity whereas chicken LHRH II (His5, Trp7, Tyr8-LHRH) was 8-9 times more potent. The LHRH agonist (Trp6, Pro9-NEt-LHRH) had 15 times greater potency than chicken LHRH I. Pre-incubation with an LHRH antagonist (D-Phe2, D-Trp6-LHRH) significantly suppressed LH release. Acid extracts of median eminence released LH from pituitary cells, extracts from short-day and long-day males had equal activity, while tissue extracts from castrated males had significantly greater LH-releasing activity. Pituitary cells from sexually immature males released LH in response to chicken LHRH I in a similar profile to cells from mature males. These data indicate that the quail LHRH receptor in the male recognizes several different molecular species of LHRH and the response to LHRH is comparable between short- and long-day males. Pituitary cells from ovulating females were variably sensitive to LHRH peptides, possibly due to changes in pituitary sensitivity during the ovulatory cycle. Pituitary cells from immature females did not release LH in response to chicken LHRH I. However, pituitary cells from immature females photostimulated for 1 wk displayed a response to chicken LHRH I and II similar to that of pituitary cells from males.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1986

Isolation, purification, and the sequence of relaxin from spiny dogfish (Squalus acanthias).

A relaxin-like molecule has been isolated from the ovaries of the spiny dogfish (Squalus acanthias) which consists, like porcine relaxin, of two chains linked by the insulin-type disulfide bonds. The total number of amino acids is 54 of which 24 are in the A chain and 30 in the B chain. The molecular masses, calculated from the amino acid compositions, are 2510 Da for the A chain and 3370 Da for the B chain, making a total of 5880 Da. The N-terminus of the B chain is protected by a 5-oxoproline (pyrrolidone carboxylic acid) residue which is also found in the same position in the relaxins of sand tiger shark, pig, and man, whereas the relaxin of the rat has its 5-oxoproline residue at the N-terminal of the A chain. By all available criteria, S. acanthias relaxin is a typical member of the relaxin family although the sequence homology to mammalian relaxins is limited to about 45% of its amino acid residues. In contrast, the dogfish relaxin shows about 80% homology with sand tiger shark relaxin (the first such interspecies similarity to be observed) and has about twice the biological activity (mouse pubic symphysis test) when compared to sand tiger relaxin.

Amino Acid Sequence↗
PubMed1986

Progesterone receptors in the oviduct of a viviparous snake (Nerodia): correlations with ovarian function and plasma steroid levels.

The physiological significance of progesterone during gestation in viviparous reptiles is not understood, although there is strong evidence for luteal synthesis and secretion of this steroid. In a previous study we characterized an oviduct progesterone receptor in the viviparous snake, Nerodia, and in this study we describe changes in receptor during the reproductive cycle. Correlation of the amount of receptor with changes in plasma estradiol 17 beta and progesterone and the effect of injected hormones suggest that the receptor may be regulated by these steroids as in mammals. Thus, the basis exists for target organ responses to progesterone and provides additional evidence for the potential role of progesterone in the early hormonal adaptations in the evolution of viviparity.

Animals↗
PubMed1986

Identification of a putative progesterone receptor in the oviduct of a viviparous watersnake (Nerodia).

The steroid hormone progesterone is of particular interest in reproductive tract adaptations associated with the processing of embryonic materials in the evolution of viviparity. To further understand the mechanisms of action of this steroid, a progesterone receptor-like moiety was partially characterized in the oviduct of the viviparous snake Nerodia. Using DNA-cellulose and LH-20 column chromatography, a binding component was identified which exhibits high affinity (KA = 1.5 X 10(9) M-1) and low capacity (approximately 10(-11) M) binding of the synthetic progestin, R5020. In addition, the binding exhibited physiological steroid specificity, and was only identified in reproductive structures considered targets of progesterone action. These characteristics are consistent with the primary characteristics associated with steroid-receptor binding and are similar in both cytosolic and nuclear extract preparations.

Androgens↗