Search PubMed⌕ Search

Biomedical subjects

J C Porter

Publications and source records attributed to J C Porter.

At least 145 records · Page 8Linked to original sources
PubMed1979

Estrogen inhibition of dopamine release into hypophysial portal blood.

The hypothesis that 17 beta-estradiol suppresses dopamine secretion into hypophysial portal blood was tested. Portal plasma concentrations of dopamine were significantly lower in proestrous rats (1.0 +/- 0.1 ng/ml; mean +/- SE) than in estrous rats (1.9 +/- 0.38 ng/ml). To deplete the animal of endogenous steroid hormones, proestrous rats were adrenalectomized (Adx) and ovariectomized (Ovx). Twenty-four hours later, hypophysial portal blood was collected for 60 min, and the plasma from this blood was analyzed for dopamine. Arterial plasma from these rats was assayed for 17 beta-estradiol and progesterone. The concentrations of dopamine in the portal plasma of sham-operated rats and bilaterally Adx-Ovx rats were similar to those in estrous animals. The concentration of dopamine in portal plasma of Adx-Ovs rats injected 24 h earlier with 50 micrograms 17 beta-estradiol was 1.0 +/- 0.31 ng/ml, which was comparable to that in proestrous animals but less than that in the estrous rats. The concentrations of 17 beta-estradiol in arterial plasma were as follows: 24 +/- 8.3 pg/ml in proestrous rats, 40 +/- 2.9 pg/ml in estrous rats, 10 +/- 1.3 pg/ml in Adx-ovx rats, and 96 +/- 17.3 pg/ml in Adx-Ovx rats injected with 50 micrograms 17 beta-estradiol. Twenty-four hours after injection of 25 micrograms 17beta-extradiol into Adx-Ovx rats, the plasma 17beta-estradiol levels were 51 +/- 7.4 pg/ml, and the dopamine concentrations in portal plasma were 1.9 +/- 0.57 ng/ml. It is concluded that an acute effect of 17 beta-estradiol is suppression of hypothalamic secretion of dopamine into hypophysial portal blood.

Adrenalectomy↗
PubMed1979

Stimulation of dopamine release into hypophysial portal blood by administration of progesterone.

To test the hypothesis that progesterone is involved in the regulation of dopamine release into hypophysial portal blood, female rats were adrenalectomized and ovariectomized at 1200 h on the day of proestrus and, immediately after the operation, injected sc with sesame oil or progesterone. Approximately 24 h later, hypophysial portal blood was collected and the plasma from this blood was analyzed for dopamine. The concentration of dopamine in portal plasma from rats given sesame oil or progesterone (50 mg) was 1.8 +/- 0.24 or 6.0 +/- 1.2 ng/ml (mean +/- SE), respectively. At the time of collection of portal blood, the progesterone concentration in arterial plasma was less than 0.8 ng/ml in rats given sesame oil and was 93 +/- 11 ng/ml in animals given progesterone. Conversely, the circulating concentrations of PRL was less (25 +/- 3 ng/ml) in animals given progesterone and higher (42 +/- 5 ng/ml) in animals given sesame oil. Twenty-four hours after the injection of progesterone (50 mg) into intact proestrous rats, the dopamine concentration in portal plasma was 5.8 +4- 1.29 ng/ml, a concentration which was significantly (P less thann 0.01) higher than that in untreated proestrous rats (1.1 +/- 0.24 ng/ml) but only slightly higher than that in untreated estrous rats (3.7 +/- 1.0 ng/ml). It is proposed 1) that progesterone administered sc can lead to an increased secretion of dopamine into hypophysial portal blood and 2) that the increased concentration of dopamine in portal plasma of intact pregnant rats relative to that of proestrous rats is, in part, a consequence of augmented progesterone secretion.

Adrenalectomy↗
PubMed1979

Subcellular localization of dopamine in the anterior pituitary gland of the rat: apparent association of dopamine with prolactin secretory granules.

The subcellular compartmentalization of endogenous dopamine in the anterior pituitary gland of the rat was investigated using continuous sucrose density gradient centrifugation. When anterior pituitary homogenates were layered on continuous sucrose density gradients (1.0--2.0 M) and centrifuged for 60 min at 40,000 X g, dopamine recovered from the gradients was associated with two sets of subcellular particles. The particles in one set were recovered near the top of the gradient, whereas those in the other set were recovered near the bottom of the gradient in the region where particles containing PRL were also found. In fact, these dense dopamine-containing particles could not be separated from those particles which contained PRL. These findings were suggestive that dopamine and PRL were present in the same particle, viz. the PRL secretory granule. This interpretation was further strengthened when it was established that the PRL-containing granules were separable on the gradient from granules which contained GH, LH, FSH, ACTH, and TSH. When [3H]dopamine was added to the solution in which the anterior lobes were homogenized, no radio-activity was found to be associated with the dense dopamine-containing particles. Also, the addition of a large excess of nonradiolabeled dopamine at the time of homogenization did not influence the amount of dopamine associated with the dense particles. Thus, the apparent association of dopamine with PRL secretory granules was not an artifact of the homogenization process per se. Therefore, it is concluded that an association exists between intracellular dopamine and the PRL secretory granule.

Adrenocorticotropic Hormone↗
PubMed1979

The role of serum lipoproteins in steroidogenesis by the human fetal adrenal cortex.

In the present investigation it was found that human fetal adrenal tissue maintained in organ culture secreted appreciable quantities of dehydroisoandrosterone sulfate (DS) and cortisol. Pregnenolone was also secreted in significant amounts, principally as the sulfate ester. The highest rate of secretion of these steroids by fetal adrenal tissue occurred when both ACTH and whole human serum were present in the culture medium. In the absence of ACTH, steroid secretion was low. When whole serum was replaced by lipoprotein-poor serum, the steroidogenic response to ACTH was markedly attenuated but not abolished. On the basis of these findings, it is concluded (1) that the human fetal adrenal can synthesize steroid hormones de novo from cholesterol, (2) that ACTH is an important stimulant of steroidogenesis by the human fetal adrenal, and (3) that plasma lipoproteins are a major source of the cholesterol utilized by the human fetal adrenal for steroidogenesis. Hence, it is likely that factors which regulate the production of fetal plasma lipoproteins are important determinants of fetal adrenal steroidogenic activity.

Adrenal Cortex Hormones↗
PubMed1979

Plasma levels of adrenocorticotropin and cortisol in women receiving oral contraceptive steroid treatment.

The secretion rate and plasma concentration of the adrenocortical steroid cortisol is modified in subjects treated with estrogenic and/or progestational steroids. The effects of contraceptive steroids on the secretion of ACTH are poorly documented, however, In the current investigation, we found that concentrations of ACTH and cortisol in plasma obtained at 0800--0900 h from a group of women with normal cyclic menses (n = 4) ranged from 78--120 pg/ml and 77--137 ng/ml, respectively. Although significant cyclic changes in the plasma levels of LH, FSH, 17 beta-estradiol, and progesterone occurred during the ovarian cycle, no obvious cyclic fluctuations in plasma levels of ACTH or cortisol were observed. In women treated with Norinyl 1 + 80 (1.0 mg norethindrone plus 0.08 mg mestranol), plasma concentrations of LH, FSH, 17 beta-estradiol, and progesterone were significantly lower (P less than 0.001) than plasma levels of these hormones in normal women during the ovarian cycle. The mean daily plasma concentrations of ACTH were significantly lower (P less than 0.001), whereas plasma cortisol levels were significantly higher (P less than 0.001) in women treated with oral contraceptive steroids compared to the levels of these hormones in the untreated ovulatory women.

Adrenocorticotropic Hormone↗
PubMed1978

Analysis of secretory patterns of prolactin and gonadotropins during twenty-four hours in a lactating woman before and after resumption of menses.

Twenty-four hour secretory patterns of prolactin, luteinizing hormone (LH), and follicle-stimulating hormone (FSH) were obtained on two separate occasions from a woman with late physiologic lactation. The studies were performed 26 and 34 months after her child's birth. During the initial study, she had amenorrhea, and her child suckled 13 per cent of the 24 hour period (Study 1). At the time of the second study, she had resumed regular menses and her child suckled for 7 per cent of the 24 hour period (Study 2). The average concentrations of prolactin during Studies 1 and 2 were 40 +/- 1.0 (mean and standard error; No. = 72) and 31 +/- 1.4 ng. per milliliter, respectively. The mean plasma prolactin concentration in Study 1 was significantly greater than that in Study 2 (p less than 0.001). The plasma concentrations of LH and FSH were significantly less in Study 1 than in Study 2 (p less than 0.001 and less than 0.01, respectively). It is concluded that hyperprolactinemia and hypogonadotropinemia were endocrinologic correlates of the amenorrhea of late physiologic lactation in this woman.

Adult↗
PubMed1978

Catechol-O-methyltransferase activity in erythrocytes of pregnant women.

Catechol-O-methyltransferase (COMT) is the enzyme that converts catechols, e.g., catecholamines and catechol estrogens, to their methyl ethers. COMT activity measured in erythrocytes (RBC's) of healthy men (No. = 47) and healthy nonpregnant women (No. = 53) was 8.2 +4- 0.17 nmoles X ml.-1 (mean and standard error). The COMT activity in RBC's of healthy pregnant women (No. = 100) was 10.7 +/- 0.29 nmoles X ml.-1 RBC X hr.-1, a value which is significantly higher than that found in RBC's of men and nonpregnant women (p less than 0.001).

Adolescent↗
PubMed1978

Effect of obesity on conversion of plasma androstenedione to estrone in postmenopausal women with and without endometrial cancer.

The purpose of this study was to ascertain if a relationship exists between the transfer constant of conversion of plasma androstenedione to estrone ([rho]AE1BU) and total body weight or excessive body weight in 50 postmenopausal women, of whom 25 had adenocarcinoma of the endometrium and 25 had no endometrial disease. The [rho]AE1BU ranged from 0.015 to 0.129 in these 50 women. The [rho]AE1BU in the women with endometrial cancer was 0.051 +/- 0.006 (mean +/- S.E.), whereas that in the women with no endometrial disease was 0.039 +/- 0.004. These values are not significantly different (p greater than 0.05). The body weights of these 50 women ranged from 104 to 430 pounds. The weight of the patients with endometrial cancer was 234 +/- 16 pounds (mean +/- S.E.), and that for the women with no endometrial disease was 194 +/- 12 pounds. A statistically significant correlation (p less than 0.001) was found between [rho]AE1BU and body weight and between [rho]AE1BU and excessive body weight in both groups of women. Moreover, obesity and aging appear to act in concert to potentiate the conversion of plasma androstenedione to estrone in extraglandular sites since the [rho]AE1BU is considerably greater among obese postmenopausal women than among comparably obese premenopausal women.

Adenocarcinoma↗