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Biomedical subjects

J R Porter

Publications and source records attributed to J R Porter.

At least 91 records · Page 5Linked to original sources
PubMed1981

The effect of cholecystokinin octapeptide on pituitary-adrenal hormone secretion.

The purpose of this investigation was to determine the influence of cholecystokinin octapeptide (CCK-OP) on pituitary-adrenal hormone secretion. CCK-OP at a dose of 5 microgram/kg (i.p.) elevated plasma corticosterone from 27 to 43 microgram/100 ml in one experiment and from 12 to 50 microgram/100 ml in a second experiment. Lower doses of CCK-OP (0.5 microgram/kg) elevated corticosterone from 12 microgram/100 ml to 20 microgram/100 ml. CCK-OP (1, 10, and 100 ng/ml) had no effect on ACTH-induced corticosterone released by isolated adrenal cells in vitro when tested in the presence of 50 pg of ACTH1-24. 100 and 500 ng of CCK-OP resulted in an increased pituitary ACTH release equal to 123% (n.s.) and a 206% (P less than 0.05) of control, respectively. In comparison, a 3/5 hypothalamic stalk median eminence equivalent increased ACTH release to 313% of control (P less than 0.05). The exact mechanism of this CCK effect on pituitary ACTH release is unknown. Although it is likely that the direct effects on the pituitary in vitro represent a pharmacologic and not a physiologic effect of this peptide, in vivo doses are between doses used for pancreatic effects and satiety effects suggesting that there may be a physiologic stimulating action of this peptide on the hypothalamic-pituitary-adrenal axis but at a level above the adrenal and pituitary.

Adrenal Glands↗
PubMed1981

Inhibition of nitrogen fixation in alfalfa by arsenate, heavy metals, fluoride, and simulated Acid rain.

The acute effects of aqueous solutions of As, Cd, Cu, Pb, F, and Zn ions at concentrations from 0.01 to 100 micrograms per milliliter and solutions adjusted to pH 2 to 6 with nitric or sulfuric acid were studied with respect to acetylene reduction, net photosynthesis, respiration rate, and chlorophyll content in Vernal alfalfa (Medicago sativa L. cv. Vernal). The effects of the various treatments on acetylene reduction varied from no demonstrable effect by any concentration of F(-) and 42% inhibition by 100 micrograms Pb(2+) per milliliter, to 100% inhibition by 10 micrograms Cd(2+) per milliliter and 100 micrograms per milliliter As, Cu(2+), and Zn(2+) ions. Zn(2+) showed statistically significant inhibition of activity at 0.1 micrograms per milliliter. Acid treatments were not inhibitory above pH 2, at which pH nitric acid inhibited acetylene reduction activity more than did sulfuric acid. The inhibition of acetylene reduction by these ions was Zn(2+) > Cd(2+) > Cu(2+) > AsO(3) (-) > Pb(2+) > F(-). The sensitivity of acetylene reduction to the ions was roughly equal to the sensitivity of photosynthesis, respiration, and chlorophyll content when Pb(2+) was applied, but was 1,000 times more sensitive to Zn(2+). The relationship of the data to field conditions and industrial pollution is discussed.

Journal Article↗
PubMed1980

Inhibitory effects of a pineal extract on adrenal cortex. Lack of competition with ACTH.

The purpose of the present investigation was to study the mode of action of a crude aqueous pineal extract (CAPE) on corticosterone (B) production from ACTH-mediated isolated adrenal cortex cells. Corticosterone production from a heterogenous adrenal cortex cell population, isolated from 8 male Sprague-Dawley rats, was measured fluorimetrically. CAPE (25 microliters) was tested in this system using ACTH (0--5,000 pg/ml) and dibutyryl-c-AMP (0--100 nM/ml) as stimuli for a period of 1 h. In a separate experiment, CAPE (25 microliters) was administered to ACTH (50 pg/ml) stimulated adrenal cortex cells for 15, 30, 60, and 120 min incubation periods. CAPE significantly decreased B produced by adrenal cortex cells at all doses of ACTH administered. CAPE also decreased the B produced by adrenal cortex cells when dibutyryl-c-AMP was used as a stimulus. The inhibitory effect of CAPE was manifest at some point in time between 30 and 60 min. It was significant at 60 min and highly significant at 120 min. It is evident from these data that CAPE and ACTH are not competing for the same receptor site.

Adrenal Cortex↗
PubMed1979

[Not Available].

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Canada↗
PubMed1977

Effects of hypothalamic extract and corticosterone on incorporation of 14C-phenylalanine into newly synthesized ACTH-like protein in vitro.

The purpose of the present experiments was firstly, to examine the efficacy of the oxycellulose-Amberlite CG-50 extraction procedure for the isolation of rat pituitary ACTH and secondly, to study the effects of both hypothalamic extract and corticosterone on the synthesis of rat pituitary ACTH. Briefly, 'cold' rat pituitary ACTH was monitored by bioassay in each step of the isolation procedure as a function of corticosterone stimulation in incubated adrenal slices. Labeled ACTH was isolated from rat pituitaries previously incubated in vitro and obtained from adrenalectomized animals and cortisone acetate treated animals to provide further data to substantiate that the labeled isolated protein contained ACTH. Cold ACTH was detected in two purified fractions (oxycellulose and Amberlite CG-50). Adrenalectomy stimulated and cortisone acetate suppressed the incorporation of 14C-phenylalaine into the ACTH-like protein in these two fractions. A continuously increasing uptake of the label into ACTH-like protein in the isolated fractions occurred with time providing evidence that de novo synthesis had taken place. Corticosterone inhibited ACTH synthesis at both 10(-4) and 10(-6) M, whereas, hypothalamic stalk median eminence (HSME) caused a significant, but not dose-related, increase in ACTH synthesis with 3/5, 1, and 2 HSME equivalents added.

Adrenalectomy↗
PubMedDate not supplied

An automated measurement system for characterization of RF and gradient coil parameters.

A fully automated laboratory-based measurement system for characterization of coil system parameters is presented. This method uses an inexpensive personal computer (PC)-controlled stepper motor positioning system in conjunction with a network/spectrum analyzer and an analog-to-digital converter (A/D) board that allows high resolution data acquisition in an unattended manner. A graphical interface was created for complete control of stepper motor movement, measurement, and data acquisition. The system is capable of performing a wide range of measurements that can, either individually or combined, characterize radiofrequency (RF) and gradient coils used in MRI. Measurement methods, theory, and results for conductor and shield current distributions, mutual impedance, and magnetic fields are given. Comparisons with theoretical calculations are included to validate the accuracy and utility of the system.

Calibration↗
PubMedDate not supplied

Influence of bombesin, CCK, secretin and CRF on corticosterone concentration in the rat.

The ingestion of food increases adrenoglucocorticoid secretion in humans and rats and influences the circadian periodicity of ACTH and corticosterone in rats fed on restricted schedules. The purpose of this study was to determine the influence of the brain-gut polypeptides CCK33 (10 U/kg), bombesin (10 micrograms/kg) and secretin (10 U/kg) on corticosterone concentrations in fed rats. The responses were compared to that of CRF (1 micrograms/kg). All experiments were begun at 10 a.m., 3 hours after the lights came on. The rats were given single, IP injections of peptide or vehicle (1 ml/kg) then sacrificed 0, 5, 10, 15, 30 or 60 minutes later. Corticosterone was measured fluorometrically. The control injection (vehicle) alone caused a mild stress response with corticosterone levels peaking between 10 and 15 minutes after the injection then returning to baseline. Both CCK33 and bombesin significantly increased corticosterone to approximately 2.5-fold above the control level in a fashion similar to that of CRF. In all three instances corticosterone levels peaked at 30 minutes post-injection. Secretin had no effect on corticosterone secretion. None of the peptides tested stimulated in vitro corticosterone output from isolated adrenal cells. These findings indicate that both CCK and bombesin cause pituitary-adrenal activation which may be related to the response of this system to food ingestion.

Animals↗