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Biomedical subjects

R O Greep

Publications and source records attributed to R O Greep.

At least 19 recordsLinked to original sources

Whither the global population problem.

Growth of the human population has been underway for thousands of years and was never a problem until recently. It is now expanding exponentially, and today global population stands at nearly 6 billion with 97 million being added each year. Currently, overpopulation has led to serious social and environmental problems such as poverty, overcrowded slums, crime, terrorism, pollution of air and water, and depletion of the protective ozone layer. Warnings were sounded, but few listened. The enthusiasm once generated for solving the problem of too many people was short-lived. The press with puzzling abrogation of its responsibility to the public managed to allay all fears of population overgrowth. Two U.S. presidents welcomed such growth as a stimulus to economic development. Although modern contraceptives are safe, effective, and widely available, more are badly needed, but none are in the pipeline. Research is being hampered by hostile attitudes and by the high cost in time and money of bringing a new contraceptive to an uncertain market with the added threat of litigation. At the present rate of growth, the population will double in the next century. This is believed to be beyond the carrying capacity of our planet. Corrective measures by man or nature need to be undertaken.

Birth Rate↗

Ovulation in light-estrous rats induced by darkness.

Adult female rats show continual vaginal cornification and cease ovulation a few weeks after they are exposed to continuous lighting (light-estrous rats). When these rats were placed in the darkness for 10 hr, 80% of the animal ovulated approximately 46 hr later. Peripheral LH increased to a small peak immediately after placing in darkness concomitant with a decrease in pituitary LH content; a large peak, 20 times higher than the basal LH level, was observed at 20 to 22 hr. Progesterone concentration in ovarian vein blood remained at extremely low levels while estrogen levels tended to rise after small LH peak. This estrogen rise appeared to play an important role in inducing the main LH peak. Simulation of the small LH peak by low doses of exogenous LH succeeded in inducing ovulation of light-estrous rats in similar fashion to the exposure of light-estrous rats to 10-hr darkness. Therefore, the small amount of LH secretion observed after the initiation of the darkness-treatment may be considered as a trigger for the whole sequence of hormonal changes leading to ovulation.

Animals↗

Kinetic studies on 15-hydroxyprostaglandin dehydrogenase from human placenta.

The enzyme system 15-hydroxyprostaglandin dehydrogenase, which catalyzes the oxidation of the 15-hydroxy group of all naturally occurring prostaglandins, has been purified 1,270-fold by isoelectric focusing. Km values have been determined for prostaglandin E2 and NAD+ and were found to be 1 and 44 muM. The overall forward reaction was V1 = 450 nmol/min. Both the product 15-ketoprostaglandin E2 and the metabolite 13,14-dihydro-15-ketoprostaglandin E2 were noncompetitive inhibitors for the enzyme.

Alcohol Oxidoreductases↗

Prostaglandin 15-hydroxy dehydrogenase from human placenta.

The enzyme system prostaglandin 15-hydroxy dehydrogenase, which catalyzes the inactivation of all biologically active prostaglandins, has been purified 1270-fold from human placenta. Kinetic studies on the enzyme have provided information on a well-organized control mechanism to avoid prostaglandin accumulation and for a fast prostaglandin degradation. 15-Ketoprostaglandin E2 and 13,14-dihydro-15-ketoprostaglandin E2 inhibit prostaglandin 15-hydroxy dehydrogenase non-competitively with respect to prostaglandin E2. The rate equation of enzyme reaction for two substrates was used for determination of the equilibrium constant and Michaelis constants of the enzyme. The following kinetic constants for prostaglandin 15-hydroxy dehydrogenase have been found. The equilibrium constant with repect to prostaglandin E2 is 18 muM, the Michaelis constant Km for prostaglandin E2 is 1 muM for NAD+ 44muM. The inhibition constants for 15-ketoprostaglandin E2 ar Ki(slope) = 70 muM, Ki(intercept) = 150 muM, and for 13,14-dihydro-15-ketoprostaglandin E2 Ki(slope) = 80 muM, and Ki(intercept) = 150 muM. The maximal velocity for the forward reaction is V1 = 0.45 mumol/min. These kinetic data exclude a random or ping-pong mechanism, and also a Theorell-Chance type as suggested by Braithwaite and Jarabak. We propose, therefore, a sequential ordered mechanism. The isoelectric point for prostaglandin 15-hydroxy dehydrogenase is at pH 5.35, judged by isoelectric focusing.

Alcohol Oxidoreductases↗

Influence of prostaglandin F autoantibodies on the estrous cycle of the guinea pig.

Adult female guinea pigs were actively immunized with prostaglandin F-2alpha conjugated to bovine serum albumin (BSA). Control animals, immunized against BSA continued to cycle normally, while the animals immunized against prostaglandin F-2alpha stopped cycling after one to three normal cycles. Laparotomy at 30 days after the last estrus revealed no recently formed corpora lutea. During the remaining 70 days of observation the antibody titer increased to 1:700, accompanied by increasing total serum estrogens (136 pg/ml at day 100) and a slow decline in circulating progesterone levels (0.6 ng/ml at day 100). The ovaries at day 100 contained degenerated corpora lutea and luteinized follicles. The suppression of the estrous cycle in the present experiments was interpreted as resulting from prolongation of luteal function as well as from inhibition of ovulation.

Animals↗

Effects of cervical stimulation and anti-LH releasing hormone serum on LH releasing hormone content in the hypothalamus.

Hypothalamic content of LHRH was radioimmunoassayed after cervical stimulation on the morning of day of estrus' LHRH content rose 3-fold by 120 min after the stimulation, reaching a level equivalent to that of day 5 of pseudopregnancy. The increase was not steady as there were two early periods when the content did not increase. Measurement of pituitary LH content revealed a marked increase followed by a sudden decrease which corresponded respectively to the two periods when LHRH levels failed ro tise. These changes in pituitary LH level suggest that both the synthesis and release of LH in the pituitary are promoted by the action of LHRH released from the hypothalamus. LH changes in the pituitary were abolished iv injection of 2 ml LHRH antiserum at the time of cervical stimulation, but pseudopregnancy was still induced and diestrus prolonged 4 days longer than in the control group. Progestin concentrations in ovarian vein blood were comparable between anti-LHRH-treated and control groups. These results suggest that the LH released by cervical stimulation is dispensable for the induction of pseudopregnancy. The marked elevation of LHRH in the hypothalamus observed immediately after cervical stimulation must be related to the regulatory mechanism of the characteristic secretory pattern of LH during the period of pseudopregnancy.

Animals↗

The effects of cosmic particle radiation on pocket mice aboard Apollo XVII: appendix III. evaluation of viscera and other tissues.

Histopathological findings in the lungs, livers, bone marrows, small intestines, gonads, kidneys, and other tissues of the four pocket mice (Perognathus longimembris) that survived the Apollo XVII flight were evaluated in the light of their immediate environment and as targest of HZE cosmic ray particles. Results of this study failed to disclose changes that could be ascribed to the HZE particle radiation. Decreased numbers of erythropoietic cells in the bone marrow of the flight mice were probably related to the increased oxygen pressure. The small intestine showed no changes. Ovaries and tests appeared normal. Two of the three surviving male flight mice displayed early stages of spermatogenesis, just as ground-based controls did at the same season. Abnormalities were also not found in the thyroid, parathyroids, adrenals, or kidneys. The status of the juxtaglomerular apparatus could not be evaluated. The lungs exhibited nonspecific slight rections. A variety of incidental lesions were noted in the livers of both the flight mice and their controls. The heart muscle showed nothing that could be regarded as pathological. Sections of skeletal muscle examined were free from significant change.

Adrenal Cortex↗