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Biomedical subjects

D L Foster

Publications and source records attributed to D L Foster.

At least 127 records · Page 7Linked to original sources
PubMed1981

Premature seasonal inhibition of tonic LH secretion by oestradiol in the female lamb and its consequences.

Patterns of circulating LH were examined in ovariectomized lambs and adults bearing Silastic capsules containing oestradiol-17 beta and in untreated ovariectomized lambs. A decrease in serum LH in oestradiol-treated lambs occurred coincidentally with the cessation of ovulations in intact lambs and in the absence of any decrease in circulating LH in untreated ovariectomized lambs. On average, these phenomena occurred 3 weeks before the seasonal reduction in serum LH levels and onset of anoestrus in oestradiol-treated ovariectomized and intact adults, respectively. The results suggest that (1) an early seasonal increase in responsiveness to oestradiol negative feedback on tonic LH secretion is responsible for the premature cessation of ovulations in the lamb, accounting, in part, for the short breeding season during the first year of life and, in some lambs, the failure to initiate cyclicity until the second year after birth; and (2) onset of anoestrus in lambs, in contrast to puberty, is not associated with steroid-independent changes in LH secretion.

Anestrus↗
PubMed1981

Importance of variations in behavioural and feedback actions of oestradiol to the control of seasonal breeding in the ewe.

Seasonal variations in the behavioural and feedback actions of oestradiol in the ewe were examined by determining the ability of various physiological oestradiol concentrations to elicit oestrous behaviour, induce an LH surge, and suppress tonic LH secretion at four times of the year. These tests were performed in acutely ovariectomized animals pretreated with oestradiol and progesterone to minimize seasonal differences in their endocrine status. Although smaller amplitude LH surges were observed in anoestrus, the dose-response curves for the induction of LH surges were virtually identical at all times of the year. Oestradiol was slightly less effective in eliciting oestrous behaviour in anoestrus and during the transition to the breeding season than at other times. This seasonal variation was, however, observed only with relatively low oestradiol concentrations; serum oestradiol levels of 3 pg/ml or greater induced oestrus in almost all ewes regardless of season. In contrast, there was a marked seasonal change in the negative feedback action of oestradiol. In anoestrus, basal oestradiol levels of 1-3 pg/ml suppressed LH to low levels (0.3 ng/ml), whereas in the breeding season, even peak oestradiol concentrations of 10 pg/ml were not able to produce this degree of inhibition. These results thus support the hypothesis that the annual breeding cycle of the ewe is governed primarily by shifts in the extent to which oestradiol can suppress tonic LH secretion.

Animals↗
PubMed1981

Endocrine mechanisms governing transition into adulthood in female sheep.

It is proposed that the first follicular phase in the lamb is initiated when responsiveness to oestradiol inhibition of LH secretion decreases sufficiently to permit the expression of an inherent hourly LH pulse rhythm. The hourly LH pulse rhythm is believed to drive oestradiol production to levels that induce the first LH surge. This hypothesis is based upon several considerations. First, pulsatile LH secretion invariably occurs at low frequencies in immature lambs whereas hourly pulses are manifest in postpubertal lambs and mature ewes during the follicular phase of the oestrous cycle. Second, intravenous administration of LH at hourly intervals to immature lambs results in an increase in follicular size, induction of an LH surge, ovulation and corpus luteum formation. Third, hourly LH pulses will occur in the immature female if the ovaries are removed; the hourly frequency in the immature ovariectomized lamb can be reduced by exogenous oestradiol. Fourth, in the chronically oestradiol-treated ovariectomized lamb, responsiveness to oestradiol inhibition of LH secretion becomes markedly decreased during the pubertal period, and the hourly LH pulse rhythm is expressed. It is further proposed that a minimum body weight and short daylengths are necessary for the reduction in oestradiol negative feedback. With regard to photoperiod, the delay in onset of cyclicity in lambs born in the wrong season (autumn) may be due to retarded maturation or post-maturational seasonal anoestrus.

Animals↗
PubMed1980

Subunits of the H+-ATPase of Escherichia coli. Overproduction of an eight-subunit F1F0-ATPase following induction of a lambda-transducing phage carrying the unc operon.

The proton-translocating ATPase complex (F1F0) of Escherichia coli was purified after inductin of a lambda-transducing phage (lambda asn5) carrying the ATPase genes of th unc operon. ATPase activity of membranes prepared from the induced lambda-unc lysogen was 6-fold greater than the activity of membranes prepared from strains lacking the unc-transducing phage, confirming the report of Kanazawa et al. (1979) Proc. Natl. Acad. Sci. U. S. A. 76, 1126-1130). The F1F0-ATPase complex was purified in comparable yield from either enriched membranes or control membranes using a modification of the procedure reported by Foster and Fillingame ((1979) J. Biol. Chem. 254, 8230-8236). EAch of the eight subunits that had been reported as components of the F1F0 complex from wild type E. coli was overproduced in the lambda-unc lysogen. All eight subunits co-purified in the same stoichiometric proportion as in the complex purified from wild type E. coli. We conclude that all eight subunits are likely coded by the small segment of chromosomal DNA carried by the lambda-transducing phage. These experiments provide the first evidence that all eight polypeptides are authentic subunits of the ATPase complex rather than contaminants that fortuitously co-purify.

Adenosine Triphosphatases↗
PubMed1980

Energy-transducing H+-ATPase of Escherichia coli. Reconstitution of proton translocation activity of the intrinsic membrane sector.

The intrinsic membrane sector (Fo) of the H+-ATPase complex of Escherichia coli has been purified, incorporated into liposomes, and its proton-translocating activity reconstituted. The Fo sector was prepared by treating a purified, particulate, F1FO-ATPase preparation with EDTA to solubilize the F1-ATPase. The resulting particulate Fo fraction was incorporated into liposomes of E. coli phospholipids by sonication. Proton efflux from these liposomes was measured with a pH electrode after imposition of a membrane potential. The kinetics of proton efflux fits that predicted by the Goldman-flux equation. The rate of proton efflux was increased maximally more than 100-fold on incorporation of the Fo sector into the liposomes. The rate of H+ efflux varied directly with the amount of Fo material added during reconstitution. Dicyclohexylcarbodiimide blocked Fo-mediated H+ efflux. Inhibition was shown to be due to reaction of dicyclohexylcarbodiimide with a specific proteolipid subunit of Fo. The preparation of Fo used in these studies contained the three proteins that had previously been identified as likely subunits of Fo (Foster, D. L., and Fillingame, R. H. (1979) J. Biol. Chem. 254, 8230-8236). It remains to be determined whether all three components are required for reconstitution of proton translocation activity.

Adenosine Triphosphatases↗
PubMed1978

Ontogeny of pulsatile luteinizing hormone and testosterone secretion in male lambs.

The ontogeny of pulsatile LH and testosterone (T) secretion was studied in the developing male sheep. Three variables of LH secretion (frequency of LH pulses, magnitude of LH pulses, and the levels between pulses) were determined during a 6-h period at each of 1, 2, 3, 5, 7, 8, 12, and 16 weeks of age in six male lambs. Pulsatile LH secretion was evident by 1-2 weeks of age in rapidly growing lambs and by 3-7 weeks of age in slowly growing lambs. Although mean height of LH discharges increased 2-fold after the onset of pulsatile release, levels between discharges remained constant throughout the entire study. The most striking change, however, occurred in the frequency of LH discharges. The frequency increased 20-fold between weeks 1 and 8 and then decreased 3-fold between weeks 8 and 16. In each lamb, a brief (less than 3 h), but marked rise (greater than 2 ng/ml) in levels of circulating T occurred after the first observed pulse of LH. Thereafter, as the lambs became older, increased concentrations of serum T were observed only during periods of pulsatile LH secretion, the highest mean level of T occurring about 1 h after each LH peak. Administration of human chorionic gonadotropin (hCG) iv to 2-day-old males resulted in a marked increase in circulating T. A greater increment in concentrations of serum T occurred after the same absolute dose (50 IU) of hCG at 8 weeks of age than at 2 days of age. These results indicate that in the male lamb 1) pulsatile secretion of LH is initiated shortly after birth and changes in mean levels of LH are primarily a reflection of changes in frequency of LH discharges; 2) before the onset of pulsatile LH secretion, the testes are capable of responding to an exogenous LH-like gonadotropin with increased secretion of T; 3) after the onset of pulsatile LH secretion, a rise in circulating T follows each pulse of LH; and 4) an increase in capacity of the testes to secret T occurs during the first 8 weeks of postnatal life. It is concluded that the pattern of LH secretion, coupled with the capacity of the testes to secrete T, determines the pattern and magnitude of T secretion in the developing male sheep.

Animals↗
PubMed1977

A new substance resembling luteinizing hormone in the blood of rhesus monkeys.

Sera from a number of rhesus monkeys showed low or undetectable levels of LH according to radioimmunoassays which employ radioiodinated rhesus LH and antisera against rhesus LH or hCG. These same sera, when assayed by a system utilizing radioiodinated ovine LH and a unique anti-ovine LH serum which cross-reacts with LH from a variety of species, appeared to contain large and variable quantities of LH. The chromatographic behavior on Sephadex G-100 of the LH-like material in these sera was indistinguishable from that of authentic rhesus LH. Chromatographic fractions containing this LH-like material, as well as the sera from which they were derived, generated dose-response curves in the ovine:anti-ovine radioimmunoassay with steeper slopes than those produced by rhesus LH. These same chromatographic fractions had negligible activity in an alpha subunit radioimmunoassay which detects not only free rhesus alpha subunit but also the alpha component of undissociated rhesus glycoprotein hormones including LH. Treatment of these fractions with 4M guanidine-HCl produced a substance of smaller molecular size which, like rhLH beta, was active in the ovine:anti-ovine assay. A substance closely resembling the serum LH-like material but having a somewhat greater molecular size is also present in the rhesus adenohypophysis, but its relationship to the serum substance remains uncertain.

Animals↗
PubMed1977

A new concept for control of the estrous cycle of the ewe based on the temporal relationships between luteinizing hormone, estradiol and progesterone in peripheral serum and evidence that progesterone inhibits tonic LH secretion.

The temporal relationships between LH, estradiol and progesterone in peripheral serum of the ewe were characterized throughout the estrous cycle. Between successive preovulatory LH sruges, serum concentrations of LH fluctuated markedly in a manner indicative of pulsatile discharges. Mean serum LH and progesterone concentrations were inversely related, LH being highest during the early and late luteal phases of the estrous cycle and lowest in the mid-luteal phase. A progressive, 5-fold increase in serum LH concentrations occurred between the onset of the precipitous fall in circulating progesterone attendant to luteolysis and the initiation of the preovulatory LH surge. Two major increments in circulating estradiol were observed in each cycle, both occurring when serum LH concentrations were relatively high. One estradiol increment occurred during the early luteal phase, the other during the 2-3 days prior to onset of the preovulatory LH surge. The latter estradiol increment thus accompanied the progressive, 5-fold increase in circulating LH which precedes the LH surge. The observations are inconsistent with the view that tonic LH secretion in the ewe is solely a function of a negative feedback action of estradiol. Rather, the temporal relationships between circulating hormones, in conjunction with recent findings that progesterone can inhibit tonic LH secretion in the ewe, lead to the conclusion that progesterone plays a major role in the regulation of tonic LH secretion during the estrous cycle of sheep.

Animals↗