Endothelin-1 (ET-1) is involved in adrenal steroid secretion but its cell origin remains unclear. We showed, using RT-PCR the expression of the mRNAs for preproET-1 and ECE-1 in primary cultures of human adrenal cells enriched in glomerulosa cells. Since these expressions could be due to contamination of steroid secreting cells by other cells, we also used the human adrenocortical cell line H295R, which was shown to produce steroids. This cell line also expressed preproET-1-RNA and released mature ET. Functional ET receptors were shown on H295R and cultured human adrenocortical cells. These findings indicate that adrenal steroid-secreting cells synthesize and release ET-1, raising the possibility for an autocrine-paracrine effect of ET-1 on adrenocortical functions.
1 The effects of hydralazine on the vasoconstrictor responses to field stimulation of sympathetic nerves were studied in the isolated proximal segments of the rat tail artery. Vasoconstrictor responses to transmural stimulation were depressed by superfusion of hydrazine (0.3, 3 and 30 muM) in a concentration-dependent manner. The inhibition appeared slowly and was not easily reversed by washing. 2 Hydralazine (30 nM, 0.3 and 3 muM) reduced the stimulation-induced overflow of tritium from proximal and distal segments of the tail artery labelled with [3H]-noradrenaline in a concentration-dependent manner. This phenomenon appeared rapidly and was easily reversed by washing. 3 Theophylline (0.5 mM) did not affect the inhibitory effect of hydralazine on the stimulation-induced tritium efflux from the distal segment of the rat tail artery. 4 The present results indicate that hydralazine has, in addition to its action on vascular smooth muscle, a very marked effect on sympathetic nerve terminals. The mechanism of this presynaptic inhibition appears to be different from the postsynaptic effect, in view of the much shorter delay, the shape of the dose-effect curve, and the lack of interaction with theophylline.
Abstract Thrombin, a potent platelet activating agent, has previously been found to increase intracellular calcium levels and/or thromboxane A 2 synthesis in leukemic cell lines exhibiting specific markers of the megakaryocyte/platelet lineage. However, its functional role on these cells has not been defined. As thrombin is implicated in the regulation of cellular proliferation or differentiation in various other cell types, we investigated the functional effects of thrombin on the megakaryoblastic MEG‐01 cell line, and further explored its receptor coupling mechanisms on these cells. We observed that thrombin caused in 1% serum containing culture medium, a reduction in the proliferation of MEG‐01 cells, without affecting their differentiation stage as determined by the expression of platelet glycoproteins GPIIb/IIIa and GPIb, FVIII‐related‐antigen and cell‐size measurement, which are specific markers for megakaryocyte maturation. In increases in cAMP levels, and in inositol‐trisphosphate formation and intracellular Ca 2+ levels. All these responses required thrombin proteolytic activity. The lipoxygenase inhibitor, nordihydroguaiaretic acid, blunted thrombin‐induced calcium increase without affecting thrombin‐induced increase in cAMP levels, suggesting different thrombin coupling mechanisms with these two second messenger pathways. In addition, the inhibitory effect of thrombin on MEG‐01 cell growth was mimicked by cAMP level enhancing agents such as forskolin, prostaglandin E 1 and Bt 2 cAMP. These results suggest the involvement of a cAMP‐dependent mechanism in the thrombin‐induced reduction in MEG‐01 cell growth.
An unaltered platelet aggregatory response to vasopressin (VP) with a lower number of platelet VP-receptors have been described in patients with Diabetes mellitus. A possible explanation could be that the lost receptors are related to a cellular event different from aggregation. We have explored VP-induced platelet shape change in diabetic and healthy subjects. We confirmed that VP-induced aggregation was identical in control and diabetic subjects. On the other hand, the diabetic patients tested did not respond to VP in terms of platelet shape change, or presented reduced responses with respect to both EC50 and maximal shape change compared to healthy subjects. In parallel, the number of VP-receptors was reduced without any alteration in their affinity.The loss of functional shape change response to VP, combined with the decrease in the number of VP-receptors occurring in diabetic patients suggests that the two abnormalities could be related. As platelet aggregation was unaltered, there may be different receptors for shape change and aggregation. The loss of the VP-induced shape change response in diabetic patients might then result from an alteration of shape change related receptors.
This study investigated the in vitro prejunctional and postjunctional actions of hydralazine in vascular and nonvascular smooth muscle. Low concentrations (micromolar) of hydralazine blocked phenylephrine-induced increases in perfusion pressure in the innervated rat kidney, whereas high concentrations (greater than 10 microM) were required in the perfused, innervated rabbit ear artery. High concentrations of hydralazine were required to block phenylephrine-induced contractions of innervated rat vas deferens and anococcygeus muscle. After in vitro denervation, rabbit ear arteries became sensitive to low concentrations of hydralazine, but this was not observed in the rat vas deferens or anococcygeus muscle. Hydralazine (1-3 microM) was without effect on 3H-release from rat vas deferens, anococcygeus muscle and kidney previously incubated with [3H]norepinephrine. Hydralazine (1 microM) decreased field stimulation-induced 3H-release from [3H]norepinephrine-loaded rabbit ear arteries. The results from the rabbit ear artery confirm that in some vessels the presence of sympathetic nerve terminals can modify the postjunctional actions of low concentrations of hydralazine. However, the other vascular tissue studied (rat renal vascular bed) was sensitive to low concentrations of hydralazine while innervated. In conclusion, the existence of a postjunctional relaxant effect of hydralazine, observed in vitro at concentrations compatible with therapeutic blood levels found in humans, has been confirmed using two different vascular preparations. The relevance of the prejunctional effect of hydralazine remains to be ascertained.
