Biomedical subjects
Publications and source records attributed to R Weiner.
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Several studies implicate endogenously synthesized prostaglandins in the mediation of reactive hyperemic responses in the coronary, renal, and skeletal muscle circulations. We sought additional evidence to involve locally released prostaglandins in the mediation of reactive hyperemia in skeletal muscle at the level of the microcirculation. The cremaster muscle of pentobarbital-anesthetized Wistar-strain rats was prepared for direct in vivo observation and measurement of postocclusive responses of single arterioles. Responses of individual arterioles were reproducible over a 3-h test period. The postocclusion increase in diameter and the duration of response were dependent upon the duration of the occlusion. Repetitive occlusions did not influence arteriolar responsiveness to vasoactive substances. Indomethacin and 5-8-11-14-eicosatetraynoic acid, inhibitors of prostaglandin synthesis, did not affect resting arteriolar diameters; however, both drugs decreased the maximum increase in diameter and duration of the vasodilator response following release of the arteriolar occlusion. These findings suggest that in this microcirculatory bed, prostaglandins contribute little to resting vascular tone; in contrast, temporary arteriolar occlusion elicits the local release of dilator prostaglandins which contribute to the reactive hyperemic response.
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The effects of colchicine and vinblastine on tanycytes of the rat median eminence have been studied using the electron microscope. Colchicine and vinblastine were administered by intraventricular cannulation into the third ventricle and demonstrated distinct morphological effects on tanycyte microtubules. Highest drug doses administered were 50.0 mug in 5.0 mul of saline initially, followed by an additional 50.0 mug of these agents infused in a volume of 13.0 mul saline over an hour. Colchicine treatment resulted in the formation of large crystalloids within tanycytes, coincident with the disappearance of microtubules, all along the ventricular surface. Nonetheless the tanycytes appeared able to maintain a continuous, tight lining, as in controls, although some crystalloids were observed beneath the ventricular surface, either within tanycyte processes or within neuronal processes. Vinblastine treatment also resulted in the formation of identical crystalloids but at highest doses thoroughly destroyed the tanycyte lining of the median eminence and exposed cellular elements below the surface to the drug. Portal capillaries approaching the ventricular surface were generally free of any signs of drug response to either colchicine or vinblastine.
1. Recordings of individual e.p.s.p.s evoked by the action of single medial gastrocnemius Ia fibres have been made from medial gastrocnemius motoneurones. In many motoneurones the action of two Ia fibres has been observed and the properties of the e.p.s.p.s compared. 2. For sixty-three pairs of averaged e.p.s.p.s, each from the same motoneurone, the ratio of half-widths was plotted against the ratio of rise times. These results were compared with theoretical values derived from the Rall compartmental model. It was found that variations in synaptic current time courses and differences in the termination of localized synaptic terminals were not sufficient to account for all the data. 3. Amplitude and rise time were inversely related but the correlation coefficient was very low. For pairs of e.p.s.p.s in the same motoneurone the e.p.s.p. with the fast rise time was larger than that with the slow rise time in forty-eight of sixty-three cases. 4. In a given motoneurone individual e.p.s.p.s evoked by the action of different Ia fibres did not vary greatly in amplitude. The ratio of peak amplitudes was less than 3 for 86% of the pairs of e.p.s.p.s examined, and the maximum was 4-8. 5. Amplitude histograms were constructed for individual e.p.s.p.s at thirty-three synapses. Twenty-two of them could be shown to satisfy the Poisson law. The others satisfied the binomial law or neither. 6. Within a given motoneurone the amplitude of an e.p.s.p. is closely related to the mean number of quanta released but not to the amplitude of the unit e.p.s.p. produced by the action of a single quantum of transmitter.
In the isolated perfused rat liver, both 5-aminolevulinate synthetase and tyrosine aminotransferase were induced by the addition of 3.5 mmol/l allylisopropylacetamide and 58 mumol/l dexamethasone to the perfusion medium. Glucose (40 mmol/l) did not affect either the induction of these enzymes or the intrahepatic level of cyclic AMP. The results suggest that the glucose effect on the induction of 5-aminolevulinate synthetase and tyrosine aminotransferase in vivo is mediated by extrahepatic factors.
The present paper reviews several lines of investigation have provided highly suggestive evidence for an important regulatory role for prostaglandins in the microcirculation. Aside from their profound vasodepressor effects in a number of animal species, including man, and their vasodilator activity in many local circulatory beds, endogenously administered prostaglandins of the E and A type also appear to reduce vascular responsiveness to a variety of vasoconstrictor agents. Furthermore, inhibition of endogenous synthesis and release of prostaglandins leads to a potentiation of vasoconstrictor responses. Thus it appears that the release of prostaglandins, an event that accompanies or is a consequence of vasoconstriction, can moderate the constrictor response and in this manner can contribute to the control of vascular reactivity. Administration of inhibitors of prostaglandin synthesis to tissues that under basal experimental conditions release prostaglandins, causes not only a decrease in prostaglandin output but also an increase in resting perfusion pressure. These results support the concept that prostaglandins that are released are essential in the control of vascular tone and resistance. Other evidence also suggests that prostaglandins participate in a variety of vascular responses, including the mediation of bradykinin vasodilation, functional hyperemia, and reactive hyperemia.
A noncomparative, phase II clinical trial on chemotherapy of leukemias and solid tumors has been undertaken. It has been attempted: (a) to synchronize cells by a first administration of an M-dependent agent (vincristine or VM 26) which blocks them during the mitotic phase (M) (this has been verified by the mitotic index), from where they start again to go into the other phases of the cycle, more or less at the same time (this has been verified by the labeling index) and (b) to destroy a greater number of cells by a second administration of cycle-dependent or phase-dependent agent(s). Remarkable results have been obtained, the most interesting one being apparently complete remissions or regressions given by the sequence of two agents in patients who during previous trials proved to be resistent to both agents administered separately. The chemotherapy protocols thus composed are administered intermittently, comprising cycles with free intervals, the duration of which depends on the time of the bone marrow and blood restoration. The hematological, immunological, and visceral tolerance is, on the whole, satisfactory.
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Recent reports have indicated that vascular responsiveness can be altered by exogenously administered or endogenously released prostaglandins. Furthermore, in certain tissues inhibitors of prostaglandin synthesis have been shown to limit the increase in blood flow in response to bradykinin and to enhance the reduction in blood flow in response to angiotensin and norepinephrine. These findings suggest an important local circulatory role for prostaglandins. We attempted to implicate further prostaglandins in local blood flow regulation by examining the effects of indomethacin (IND) and 5,8,11,14-eicosatetraynoic acid (ETA), inhibitors of prostaglandin synthesis, on microvascular arteriolar responses to bradykinin, prostaglandin E1 (PGE1), prostaglandin E2 (PGE2), histamine, norepinephrine, and angiotensin. Male Wistar rats were anesthetized with sodium pentobarbital, and their cremaster muscle was exteriorized and prepared for in vivo microscopic observation of microvessels. Changes in arteriolar luminal diameters in response to topical administration of vasoactive agents were quantified with an image-shearing measuring eyepiece in conjunction with a television microscope and recorder. Local administration of IND or ETA significantly reduced the arteriolar dilation elicited by bradykinin, whereas the responses to PGE1 and PGE2 remained unaltered. Responses to histamine, although somewhat reduced, were not significantly different from control. Vasoconstrictor responses of arterioles elicited by norepinephrine and angiotensin were potentiated by IND or ETA administration. These results indicate that prostaglandins synthetized in skeletal muscle microcirculation in situ (1) mediate, in part, vasodilator responses to bradykinin and (2) modulate vasoconstrictor responses to angiotensin and norepinephrine. Thus, these findings support the hypothesis that prostaglandins are local regulators of microvascular responsiveness.
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Forty-three patients with chronic myeloid leukaemia have been treated with hydroxyurea in order to be subjected to leucopheresis for white cell transfusions. Hydroxyurea decreases leucocytosis when it is administered and the blood granulocyte number increases soon after the drug is stopped. The survival of the patients is not different from the survival of the patients treated with conventional chemotherapy (busulphan, mitobronitol) and it is superior to the survival of patients treated with external radiotherapy or with (32)P. Half of the patients were subjected to splenectomy during first remission for a phase II trial. They were not randomized, but the distribution according to age was similar in the two groups. A slight difference appears in favour of splenectomy so far as survival is concerned, but there were three post-operative deaths out of 18 patients. We conclude that a phase II trial on the value of splenectomy is indicated ethically, but that the patients should be operated on and nursed in a microbiologically controlled environment.
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