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M S Sheppard

Publications and source records attributed to M S Sheppard.

24 records · Page 2Linked to original sources
PubMed1981

Tetraethylammonium modifies gap junctions between pancreatic beta-cells.

Gap junctions between pancreatic beta-cells were quantitatively assessed in freeze-fracture replicas of isolated rat islets of Langerhans incubated for 90 min with or without the potassium conductance blocker tetraethylammonium (TEA). The results show that TEA increases the median number of particles per beta-cell gap junction but not the frequency of gap junctions at both nonstimulating and threshold-stimulating concentrations of glucose. TEA increased the relative gap junctional area at both concentrations of glucose. TEA had no effect on insulin release at a basal concentration of glucose but potentiated that release at the threshold glucose level. Thus TEA modifies beta-cell gap junctions independently of its effect on insulin release. However, the junctional changes observed were greater when insulin release was also elevated.

Animals↗
PubMed1980

Release of growth hormone from purified somatotrophs: interrelation between Ca++ and adenosine 3',5'-monophosphate.

cAMP is thought to be an essential intracellular mediator in the release of GH from somatotrophs. Ca++ is required in the incubation medium to elicit GH release in vitro. We have carried out studies using a purified preparation of rat somatotrophs to see whether the Ca++ requirement procedes or follows the accumulation of cAMP induced by prostaglandin E2 (which increases adenylate cyclase activity) and 3-isobutyl-1-methylxanthine (a phosphodiesterase inhibitor). Incubation of somatotrophs in low Ca++ medium (less than 85 microM) abolished the release of GH induced by the two secretagogues, while the increase in intracellular cAMP was actually augmented. Thus, Ca++ is required in the incubation medium to express the action of intracellular cAMP.

Animals↗
PubMed1979

Release of growth hormone from purified somatotrophs: role of adenosine 3',5'-monophosphate and guanosine 3',5'-monophosphate.

Studies were carried out to simultaneously measure cAMP and cGMP accumulation and GH release from acutely dispersed purified somatotrophs obtained from rat adenohypophyses. cAMP accumulation was dramatically increased by both prostaglandin E2 (10(-6) M) and 3-isobutyl-1-methylxanthine (a phosphodiesterase inhibitor, 0.5 mM) within 1 min of their addition, while there was a delay of 8--16 min before a significant increase in GH release was seen. SRIF (100, 10, or 1 ng/ml) completely blocked the stimulated release of GH. SRIF also consistently decreased the elevation of cAMP induced by the two secretagogues, but this decrease was small and not always significant. cGMP was unmeasurable (less than 0.02 fmol/1000 cells) in all of our experiments, while basal cAMP levels were about 1 fmol/1000 cells. We conclude that cAMP plays a role in the intracellular mechanisms governing GH release and that SRIF primarily acts subsequent to cAMP elevation, with a possible secondard or minor action on cAMP formation.

1-Methyl-3-isobutylxanthine↗
PubMed1975

The difference in the clearance of interstitial albumin by the lymphatics from the stomach and the small and large intestine.

The capacity of the lymphatics to clear interstitial albumin was compared between the stomach, small intestine, and colon. The lymphatic and vascular transport in the stomach and colon was similar, clearing approximately 9 per cent of interstitially injected radioiodinated serum albumin by the thoracic duct lymph and 2 to 3 per cent by the blood in a five hour period. More than a third of the injected material remained at the site of injection. The small intestine was cleared of 37 per cent of the albumin by the lymph and more than 6 per cent by the blood, leaving less than 9 per cent at the injection site in the same period of time. Evidence that the small intestine was more effective and rapid in clearing interstitial albumin than either the stomach or colon was statistically significant.

Albumins↗
PubMedDate not supplied

Innovative nuclear pharmacy service. A comprehensive management plan for clinical investigations.

OBJECTIVE: To provide an overview of the investigational nuclear pharmacy service at the Medical University of South Carolina. DATA SOURCES: References were selected from published bibliographies of nuclear pharmacy and hospital pharmacy articles and from specific-topic searches of the MEDLINE computerized database (all languages, through 1992). STUDY SELECTION: Studies of clinical pharmacy functions that were considered relevant to the specialty practice of nuclear pharmacy were chosen. DATA EXTRACTION: Studies were reviewed for internal consistency and appropriateness. DATA SYNTHESIS: Data on the clinical impact of nuclear pharmacy services do not exist. CONCLUSIONS: Based on our experience in establishing an investigational drug service, we conclude that nuclear pharmacists should take an active role in clinical investigations. The outcomes of this kind of involvement are very rewarding.

Drug Evaluation↗