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Biomedical subjects

D T Baird

Publications and source records attributed to D T Baird.

At least 307 records · Page 17Linked to original sources
PubMed1977

Pulsatile release of luteinizing hormone and the secretion of ovarian steroids in sheep during anestrus.

The peripheral concentration of LH and the secretion rates of estradiol-17beta and androstenedione were measured every 10 min for 4 h during anestrus in six ewes with utero-ovarian autotransplants. The basal concentration of LH was 0.45 +/- 0.06 ng//ml (NIH LH S14; mean +/- SEM), with pulses of LH (6.0 +/- 0.3 ng/ml; N = 5) occurring with an average frequency of one per 5 h. The basal secretion rate of estradiol-17beta was 0.5--1.3 ng/min. Each pulse of LH was followed by a rise in the secretion of estradiol-17beta. Maximum secretion of estradiol-17beta was 5.18 +/- 0.72 ng/min and was reached 25 min after LH discharge. Basal secretion of androstenedione was higher than estradiol-17beta at about 1.5 to 3.4 ng/min, and increased to a maximum 26.8 +/- 6.6 ng/min 25 min after LH discharge. Steroid secretion was not maintained at maximum rates and had returned to basal levels 2 h after LH discharge. The data show that the ovary of the anestrous sheep is capable of secreting steroids following pulses of endogenous LH. These results strongly suggest that as in the luteal phase of the cycle, the quantity of estradiol and androstenedione secreted by the ovary is related to the frequency of episodic pulses of LH.

Androstenedione↗
PubMed1977

Pituitary-ovarian relationships in polycystic ovary syndrome.

The spontaneous pattern of pituitary gonadotropins and ovarian steroids and their response to dynamic tests were measured in 12 women with polycystic ovarian syndrome (PCO) and the results compared to those from 6 normal women during the early follicllar phase of the cycle (controls). As judged by serial measurements of urinary total estrogen and pregnanediol over a 12-week period, in PCO patients 75% of cycles were anovulatory (anovulatory PCO) as compared to 100% ovulatory in controls. The basal concentrations of LH, androstenedione and estrone were significantly higher and the concentration os FSH significantly lower in anovulatory PCO than in the controls (P less than .05). In PCO patients the concentration of LH was lower following an ovulatory cycle than that following a period of anovulation. Negative and positive feedback responses to an estrogen provocation test (200 microgram ethinyl estradiol per day for 3 days) were normal in anovulatory PCO although the LH peak occurred 24 h earlier than in the controls. The amplitude of the pulses of LH was significantly greater in anovulatory PCO than in the controls and was suppressed in both groups after ethinyl estradiol. The peak release of LH in response to 56 microgram LRF in ovulatory PCO was similar in controls but LH responses in anovulatory PCO were significantly greater. It is suggested that the abnormalities in gonadotropin secretion in PCO are secondary to excessive and prolonged extraglandular production of estrogen from androstenedione.

Adult↗
PubMed1977

Seasonal variation in oestrus, the secretion of oestrogen and progesterone and LH levels before ovulation in the ewe.

Ewes with cervical ovarian autotransplants were studied after PGF-2alpha-induced luteal regression in November and February (mid- and late-breeding season) and June (anoestrum). Progesteron and oestradiol-17beta secretion rates and LH concentrations were determined in serial ovarian venous blood samples and the ewes were frequently tested for oestrus. All 4 ewes in November and 3 of the 4 ewes in February exhibited oestrus and endocrine changes indicative of ovulation. The remaining ewe in February and the three ewes in June failed to show elevated oestradiol-17beta secretion rates after luteal regression, indicating the absence of follicles in the final stages of maturation. The preovulatory rise in the oestradiol-17beta secretion rate, the LH surge and the display of oestrus all occurred earlier, with respect to the PGF-2alpha infusion, in November than in February, suggesting a greater stimulation of folliculogenesis, and therefore a greater availability of maturing follicles, in November than in February.

Animals↗
PubMed1977

Simultaneous infusion of prostaglandin E2 antagonizes the luteolytic action of prostaglandin F2alpha in vivo.

Corpora lutea of ewes bearing ovarian autotransplants were infused for 4 h with prostaglandin F2alpha (PGF2alpha) (10 microng/h), PGF2alpha+PGE2 (10microng/h of each), PGE2 (10 microng/h) or saline on day 10 of the cycle. Ovarian venous blood obtained before, during, and up to 12 h after the infusion period, was assayed for progesterone. Prostaglandin F2alpha produced an immediate, rapid and sustained decline in progesterone secretion, but infusion of PGE2 together with PGF2alpha prevented the decline until after the infusion. Progesterone secretion was unaffected by infusion of PGE2 alone. Oestrous behaviour was observed in four out of seven animals infused with PGF2alpha but in only one out of six infused with PGF2Alpha+PGE2. None of the animals infused with PGE2 alone or saline only came into heat.

Animals↗
PubMed1977

Concentration of prostaglandin F2alpha and steroids in the human corpus luteum.

The concentration of prostaglandin F2alpha (PGF2alpha), progesterone, pregnenolone, oestradiol-17beta, oestrone, androstenedione and testosterone was measured in corpora lutea obtained from 40 women at various stages of the menstrual cycle. The concentration of PGF2alpha was significantly higher in corpora lutea immediately after ovulation (26-7 +/- 3-9 (S.E.M.) ng/g, P less than 0-005) and in corpora albicantia (16-3 +/- 3-3 ng/g, P less than 0-005) than at any other time during the luteal phase. There was no correlation between the concentration of PGF2alpha, and that of any steroid. The progesterone concentration was highest in corpora lutea just after ovulation (24-9 +/-6-7 microng/g) and in early luteal groups (25-7 +/- 6-8 microng/g) but declined significantly (P less than 0-05) to its lowest level in corpora albicantia (1-82 +/- 0-66 microng/g). The concentration of oestradiol-17beta in the corpus luteum and luteal weight were significantly greater during the mid-luteal phase than at any other stage (concentration 282 +/- 43 ng/g), P less than 0-05; weight 1-86 +/- 0-18 g, P less than 0-005). The results indicate that regression of the human corpus luteum is not caused by a rise in the ovarian concentration of PGF2alpha in the late luteal phase of the cycle.

Adult↗
PubMed1976

Pulsatile release of LH and secretion of ovarian steroids in sheep during the luteal phase of the estrous cycle.

The concentration of LH and progesterone in jugular venous plasma and the secretion of steroids by the ovary were measured every 10 minutes for 2 hours on days 12, 14, and 16 of the estrous cycle in 5 ewes with utero-ovarian autotransplants. A pulse of LH occurred about once every 2 hours, when the concentration rose from a basal level of 0.57 +/- 0.08 ng/ml to a peak of 2.97 +/- 0.57 ng/ml. Within 5 minutes of the pulse of LH, the secretion of estradiol (an exclusive product of the follicle) rose rapidly from a basal level of 0.75 +/- 0.12 ng/min to reach a peak value of 2.16 +/- 0.33 ng/min in about 30 minutes. In contrast, the secretion of progesterone from the corpus luteum, and the concentration of progesterone in the peripheral plasma changed very little following the pulse of LH. The secretion of androstenedione, which arises from the follicle and corpus luteum, increased from 3.03 +/-0.75 ng/min to 7.85 +/- 1.78 ng/min by 30 minutes after the pulse of LH. These findings indicate that the follicle, and possibly the stroma, respond rapidly to episodic fluctuations in the concentration of LH and are probably involved in the negative feedback loop between the ovary and the hypothalamic pituitary system. The fluctuations in the secretion of progesterone from the corpus luteum, on the other hand, are unrelated to pulses of LH.

Androstenedione↗
PubMed1976

The source of ovarian oestradiol and androstenedione in the sheep during the luteal phase.

The secretion of oestradiol and androstenedione was investigated in sheep by cannulating both ovarian veins in situ. The mean ovarian blood flow (ml/min +/- SE) was significantly higher on the side containing the corpus luteum (7.67 +/- 1.36) than on the contralateral side (4.93 +/- 0.85). The mean secretion (ng/min +/- SE) of oestradiol (1.09 +/- 0.36) and androstenedione (1.52 +/- 0.16) was higher on the side containing at least one large follicle (diameter greater than 4 mm) than on the contralateral side (0.19 +/- 0.05 and 0.62 +/- 0.21, respectively). The secretion of oestradiol was unchanged following enucleation of the corpus luteum but fell to very low levels (0.062 +/- 0.022 ng/min) after enucleation of follicles diameter greater than 4 mm. The secretion of androstenedione fell significantly after enucleation of both corpus luteum and largefollicles. These results suggest that during the luteal phase in the sheep oestradiol is secreted virtually exclusively by the largest non-atretic Graafian follicle. Androstenedione in contrast arises from both follicle, corpus luteum and possibly stroma.

Androstenedione↗
PubMed1976

The oestrous cycle of the ewe after active immunization against prostaglandin F-2 alpha.

Six ewes were immunized against a prostaglandin F-2alpha-protein conjugate. Between 24 and 82 days after immunization the regular cyclic occurrence of oestrus was abolished in all six ewes. Further investigations of the immunized animals revealed that the blockade of oestrus was due to a persistence of the CL and the constantly elevated (greater than 2 ng/ml) blood levels of progesterone. Surgical enucleation of the persistent CL was promptly followed by a fall in progesterone concentrations (less than 0-5 ng/ml), normal oestrus and a subsequent return to a state of constantly elevated blood progesterone levels. These results show that neutralization of the biological activity of PGF by active immunization against PGF-2alpha results in a failure of luteal regression and provide evidence that endogenous PGF is involved in normal luteal regression in this species.

Animals↗
PubMed1976

Dynamic studies of prostaglandin F-2 alpha in the utero-ovarian circulation of the sheep.

The concentration of prostaglandin (PG) F-2alpha in ovarian arterial blood was compared to that in aortic and carotid blood at different stages of the ovine oestrous cycle, and its concentration measured in the ovarian artery following the infusion of radioactive PGF-2alpha to the uterine vein. In all cases the concentration of PGF-2alpha increased during passage through the ovarian artery, and the increase was proportional to the log of the concentration in the uterine vein. No such change was observed in the concentration of progesterone in the ovarian artery or of PGF in the uterine artery. It was concluded that PGF-2alpha can be and is normally transferred from the uterine vein to the ovarian artery. These results are compatible with the hypothesis that PGF-2alpha of uterine origin is the normal luteolytic agent in the sheep.

Animals↗
PubMed1976

Androstenedione and the control of luteinizing hormone in the ewe during anoestrus.

Androstenedione and oestradiol were measured by radioimmunoassay in the utero-ovarian venous plasma of two ewes during anoestrus. The concentrations of both steroids were significantly higher than the corresponding concentrations in peripheral plasma, indicating that androstenedione and oestradiol are secreted by the ovary during anoestrus. The concentration of LH during anoestrus was measured by radioimmunoassay in jugular venous plasma of control ewes, ewes immunized against 11alpha-OH-androstenedione-bovine serum albumin and ewes that had been ovariectomized and hystrectomized 9 months previously. During a 12 h sampling period, discharges of LH occurred more frequently in the immunized ewes than in the control group but less frequently than in the ovariectomized group. The frequency of discharge was positively correlated with the titre of androstenedione antibodies in the immunized animals. After injection of 25 mug oestradiol benzoate (OB) all controls, 3 out of 5 immunized and 4 out of 5 ovariectomized-hysterectomized ewes showed positive feedback. No positive feedback occurred in the two ewes with the highest antibody titres to androstenedione, but negative feedback in response of OB apperaed to function normally in all the androstenedione immunized sheep. It is postulated that androstenedione, or one of its metabolites, normally modulates the effects of oestradiol in the control of gonadotrophin secretion in the ewe.

Androstenedione↗