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Biomedical subjects

G A Morrill

Publications and source records attributed to G A Morrill.

12 recordsLinked to original sources
PubMed1979

Studies on the relative roles of pituitary and progesterone in the induction of meiotic maturation in the amphibian oocyte.

In the amphibian, gonadotropins act on the epithelial cells surrounding the oocyte to produce and/or release progesterone which in turn acts at the oocyte surface to initiate the resumption of meiotic maturation. Since maturation is reported to require continuous exposure to gonadotropins but only brief (5--15 min) exposure to progesterone, it was of interest to reexamine the interrelationships between the two hormonal stimuli as well as the kinetics of progesterone production, metabolism, and biological activity. Germinal vesicle breakdown (GVBD) required continuous exposure to 0.005 pituitaries/ml for 6.0 h to produce 50% GVBD that occurred at 10.1 h. Actinomycin D (10 microgram/ml) completely inhibited pituitary induced GVBD when added during the first 5--6 h; 50% inhibition occurred when added at 7.3 h. Thus, actinomycin D continues to inhibit 1--2 h after the requirement for pituitary stimulation. Pituitary stimulation produced a 4-fold increase in 3H-acetate incorporation into progesterone and acetate conversion to progesterone was relatively constant during successive 2 h pulses throughout the 10 h period leading to GVBD. There was no significant metabolism of 3H-acetate derived progesterone when follicles were treated with pituitary extract, although the same follicles rapidly concentrated and metabolized exogenous 3H- or 14C-progesterone. The length of continuous progesterone exposure required for 50% GVBD varied from 11 h at 0.158 microM to less than 0.08 h at 15.8 microM. The time to 50% GVBD was only delayed by about 10% (1.5 h) when maximal and minimal progesterone levels were compared. A comparison of 3H-progesterone uptake and response (GVBD) as a function of [progesterone]0 indicated that uptake of 2--4 mumol 1(-1) cell water will induce 50% GVBD. These results indicate that a threshold uptake must be reached to initiate resumption of meiosis and that this level must be maintained throughout the period leading to nuclear breakdown. Under physiologic conditions, gonadotropins stimulate progesterone production and this progesterone is protected from, or inaccessible to, steroid metabolizing enzymes.

Animals↗
PubMed1978

Effect of colchicine on estrogen action. I. Inhibition of 17 beta-estradiol-induced water and potassium uptake in the immature rat uterus.

The effects of colchicine on 17 beta-estradiol-induced water and electrolyte uptake in the uterus of the immature rat have been examined 6 h after treatment with this estrogen. Estradiol stimulates an increase in total uterine Na+, K+ and water while intracellular Na+ and K+ concentrations remain relatively unchanged. Assuming the sodium space is equivalent to the extracellular space, the extracellular fluid compartment increases about 84% in response to estradiol. Similarly, the intracellular compartment increases by about 62%. The uptake of water into the cellular compartment may be a direct response to a stimulation of K+ accumulation by uterine cells. Colchicine inhibits both estradiol-induced rise in intracellular potassium and both intra- and extracellular water.

Animals↗
PubMed1977

An analysis of transport, exchange, and binding of sodium and potassium in isolated amphibian follicles and denuded oocytes.

The uptake and efflux of 22Na and 42K were studied in fully grown, prophase-arrested Rana pipiens follicles and denuded oocytes. Follicles and denuded oocytes contained large stores of both cations, although only 15--30% of the total Na+ and 1--2% of the total K+ pools exchanged within the 12-h period studied. 22Na uptake and efflux in follicles exhibited two-step kinetics with a smaller rapidly exchanging fraction (12--15%, t0-5 approximately 15 min), and a larger slow fraction (t0-5 approximately 0-5 day). Denuded oocytes displayed a single kinetic fraction with a rate constant similar to the slow fraction of follicles, suggesting that the fast fraction was associated with the follicular epithelium. Both follicles and denuded oocytes exhibited fast and slow 42K uptake kinetic fractions, although the follicular fast fraction was considerably larger. Conversely, whereas follicular 42K efflux also proceeded with two-step kinetics, 42K efflux from denuded oocytes appeared as a single slow fraction. Thus, a large portion of the fast K+ fraction taken up by the follicles is attributable to the somatic cells of the follicular envelopes. Na+ and K+ activities were measured in the cytoplasm of the in situ (follicular) oocyte using cation-selective microelectrodes. After correcting for Na+ and K+ associated with the follicular envelopes, only about 6% of the total ooplasmic Na+ and less than 1% of the K+ could be accounted for as bound or sequestered.

Animals↗