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Biomedical subjects

I P Callard

Publications and source records attributed to I P Callard.

At least 73 records · Page 4Linked to original sources
PubMed1979

Plasma levels of vitellogenin in Chrysemys picta during the annual gonadal cycle: measurement by specific radioimmunoassay.

A RIA for turtle (Chrysemys picta) vitellogenin is described. After dimethylformamide precipitation of vitellogenin from the plasma of estrogen-treated female turtles, antibodies were developed in rabbits. The dimethylformamide precipitate was further purified by o-triethylaminoethyl cellulose column chromatography; the vitellogenin component eluted as a single peak. This material was used for iodination by a mild chloramine method. Antibodies to turtle vitellogenin did not cross-react with plasma from male turtles or vitellogenic females of other vertebrate groups, including lizards and snakes. Limited cross-reactivity exists among the chelonians, however. Using a 1:5000 dilution of antiserum, the limit of detection was 15 ng, and the midrange was 320 +/- 45 ng. For an antiserum dilution of 1:1000, these figures were 30 and 600 +/- 37 ng, respectively. Using this assay, the seasonal pattern of plasma vitellogenin in the turtle has been described, and preliminary studies on in vitro hepatic vitellogenesis have been performed.

Animals↗
PubMed1979

Estrogen-binding proteins in the oviduct of the turtle, Chrysemys picta: evidence for a receptor species.

Estradiol-binding proteins in the reproductive tract of the turtle, Chrysemys picta, were characterized. Cytosol was prepared from the oviducts of mature female turtles, and estradiol binding was measured using charcoal adsorption and glycerol density gradient centrifugation. A sex steroid-binding protein (SBP) similar to that found in turtle plasma was demonstrated in oviduct cytosol. The characteristics of this SBP-like binding were as follows: Ka = 10(8) M-1; capacity, 10(-12) mol/mg protein; and sedimentation coefficient, 6--7S in low salt gradients. The SBP-like protein binds testosterone and progesterone as well as 17 beta-estradiol but does not bind diethylstilbestrol. No receptor-like binding activity could be demonstrated using these techniques. Explant culture and DNA cellulose affinity chromatography were used to remove the SBP-like material before assay of [3H]estradiol binding. Using these techniques, a high affinity (Ka = 10(9) M-1), low capacity (n = 10(-14) mol/mg cytosol protein) estradiol receptor was demonstrated. The putative turtle receptor exhibits steroid specificity and sedimentation profiles (6S and 8S in low salt, 4S and 5S in high salt) comparable to those of estrogen receptors in mammalian species. These results suggest a certain degree of physiochemical similarity between putative estrogen receptors in mammalian and turtle reproductive tracts.

Animals↗
PubMed1976

The influence of oestradiol-17beta and progesterone on the contractility of the oviduct of the turtle, Chrysemys picta, in vitro.

The contractility of the oviduct of Chrysemys picta (the fresh-water turtle) was studied in vitro. Significant regional differences in contractile activity were observed. Contractions increased in amplitude and duration and decreased in frequency from the proximal to the distal end of the oviduct. Injections of oestradiol-17beta in vivo increased the amplitude of contractions and decreased the duration of the rest period in segments taken from the diatal end of the oviduct. In contrast, progesterone injections significantly reduced the duration of both contractile and resting periods.

Animals↗