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D Delbeke

Publications and source records attributed to D Delbeke.

62 records · Page 4Linked to original sources
PubMed1983

Effect of thyrotropin-releasing hormone on dog thyroid in vitro.

The in vitro action of thyrotropin-releasing hormone (TRH) on the cyclic AMP level and iodine metabolism in dog thyroid, has been studied. TRH inhibited cyclic AMP accumulation and subsequent secretion in slices stimulated by thyrotropic hormone (TSH), prostaglandin E1, cholera toxin and to a lesser extent forskolin. The effect of TRH was suppressed in a medium deprived of calcium or in the presence of isobutylmethylxanthine. TRH also stimulated iodide binding to proteins, but not cyclic GMP accumulation. Although all these characteristics of TRH action on dog thyroid fit those of prostaglandin F1 alpha in this tissue, TRH effects were not relieved by indomethacine. The possibility of a TRH action through other known inhibitors of the cyclic AMP system in dog thyroid such as: acetylcholine, alpha-adrenergic agents, adenosine, iodide were checked and ruled out. The possible involvement of other neurotransmitters, such as ATP or vasoactive intestinal peptide were studied but could not be substantiated. Our data suggest the existence of a direct negative action of TRH on the thyroid itself besides its stimulatory role at the pituitary level. The great variability of the TRH effect was overcome by pretreatment of the dog by pyridostigmine, an acetylcholinesterase inhibitor.

1-Methyl-3-isobutylxanthine↗
PubMed1983

Synthesis and biological activity of 5-fluoroimidazole-TRH.

The 5-fluoroimidazole analogue of thyrotropin-releasing hormone, obtained by total synthesis from 5-fluoro-L-histidine, neither binds to rat pituitary cells nor stimulates release of prolactin from them. Lévine-Pinto et. al. reported an agonist, which was generated during presumptive photofluorination of the hormone and which they believed to be the 5-fluoro analogue. In addition to the striking contrast in biological activities, the chemical properties of the agonist differ markedly from those of our peptide and are inconsistent with expectation for the fluoroimidazole moiety. Despite its inactivity in pituitary functions, the authentic 5-fluoro analogue mimics the natural hormone with respect to cardiovascular responses in the central nervous system.

Animals↗
PubMed1983

Alphafetoprotein (AFP), concanavalin A non-reactive AFP and specific acetylcholinesterase in amniotic fluid from pathological pregnancies. Predictive values for open spina bifida.

Alphafetoprotein (AFP) and concanavalin A non-reactive alphafetoprotein determination and the acetylcholinesterase (AchE) qualitative test have been performed on amniotic fluid samples from 33 normal pregnancies, 44 pregnancies with fetal malformations and 8 normal pregnancies with elevated amniotic fluid alphafetoprotein (3 false positive AFP results, 5 contaminations with fetal blood). The validities of these three tests in detecting abnormal pregnancies are compared. The usefulness of the existing complementary tests in the detection of neural tube defects in a low neural tube defect incidence area is discussed. Risk figures for open spina bifida according to the prior risk situation and the results of maternal serum AFP, amniotic fluid AFP, AchE qualitative test and ultrasound examination have been calculated.

Acetylcholinesterase↗
PubMed1982

Cooling enhances adenosine 3':5' monophosphate accumulation in thyrotropin stimulated dog thyroid slices.

Dog thyroid slices have been stimulated in vitro by thyrotrophin (TSH) at 37 degrees C and 25 degrees C. Adenosine 3':5'-monophosphate (cyclic AMP) accumulation was enhanced by cooling to 25 degrees C. This observation has been extended to kidney cortex slices stimulated by parathyroid hormone (PTH). However, this phenomenon is not general: it does not apply to thyroid slices stimulated by prostaglandin E1 (PGE1) or adrenal cortex slices stimulated by adrenocorticotrophic hormone (ACTH). Slight cooling provides a useful tool to influence biochemical mechanisms in intact cells and therefore the mechanism of action of cooling on cyclic AMP was investigated in dog thyroid slices stimulated by TSH. Adenylate cyclase and cyclic nucleotide phosphodiesterase activities as measured in acellular preparations decreased in parallel with the temperature. A decrease of the cyclic AMP efflux from the cell at 25 degrees C, although not measurable in this preparation, did not seem to be responsible for the phenomenon. computer simulation of the kinetics of the cyclic AP accumulation curve is compatible with the hypothesis of decrease in the desensitization rate of adenylate cyclase at 25 degrees C. This was demonstrated using an experimental protocol in intact slices and by measurements of adenylate cyclase activities in particulate preparations of slices pretreated or not by the hormone. This decreased adenylate cyclase desensitization can explain the higher cyclic AMP levels in TSH stimulated thyroid slices incubated at 25 degrees C. However, this does not exclude complementary mechanisms.

3',5'-Cyclic-AMP Phosphodiesterases↗
PubMed1981

Ultrasonic evaluation of fetal ventricular growth.

The ratio of lateral ventricle to hemispheric width was measured in 200 normal pregnancies. Statistical curve fitting was tried to predict normal value and 5 and 95 percentiles. Anatomical sections of fetal head are provided to correlate the ultrasonic pictures. A typical case of application is described.

Adult↗
PubMed1976

Kinetics of adenosine 3':5'-monophosphate accumulation in dog thyroid slices.

Dog thyroid slices have been stimulated in vitro by thyrotropin. The kinetics of adenosine 3':5'-monophosphate (cyclic AMP) accumulation due to the activation of adenylate cyclase were measured. Experimental results have been interpreted by means of a numerical simulation based on a theoretical description of the overall process which consists of three steps: (a) the penetration of thyrotropin in the slices, (b) the binding of the hormone to the specific receptor and the consequent activation of adenylate cyclase, (c) the kinetics of cyclic AMP accumulation in each cell due to the interplay between synthesis and degradation. The numerical values of the parameters needed for the simulation were deduced from separate experiments. Diffusion of thyrotropin in the slices has been calculated from the kinetics of efflux of [3H]sucrose, and with or without albumin. Adenylate cyclase activity and activation by thyrotropin in homogenates and purified membranes were measured. Binding experiments of cyclic AMP on crude extract of dog thyroid lead to the conclusion that the maximal capacity of the specific binding site is close to the cyclic AMP content in resting thyroid cells. The purpose of this paper is to verify the validity of the current concepts about the mechanisms taking place in this process by comparing experimental results and theoretical simulation. It results from the study that for this system the time between the activation of adenylate cyclase and half maximal cyclic AMPaccumulation is equal to 3 min 45 s and the pool of cyclic AMP is renewed three times per minute. It has been also stressed that the thickness of the slices as well as inhibitors of phosphodiesterases change the apparent kinetics of cyclic AMP accumulation.

Adenylyl Cyclases↗