SAPINTOXIN-A AND PHORBOL 12,13-DIBUTYRATE - 2 PHORBOL DERIVATIVES WITH CONTRASTING EFFECTS ON RAT-BLOOD VESSEL PERMEABILITY IN-VITRO

Rat isolated small intestine and mesentery were perfused with a gelati n-containing physiological salt solution, and microvascular permeabili ty in the villi was assessed using colloidal carbon as a marker to ass ess the effect of sapintoxin A in this experimental situation, and to compare it with phorbol 12,13-dibutyrate. Sapintoxin A (1, 0.25, 0.1 m u M) had no effect on colloidal carbon leakage compared with control v alues, but significantly increased perfusion pressure. Phorbol 12,13-d ibutyrate (1 mu M) significantly increased both colloidal carbon leaka ge and perfusion pressure. Pretreatment with the protein kinase C inhi bitor Ro 31-8220 (1 mu M) significantly increased colloidal carbon lea kage in the presence of sapintoxin A, but significantly decreased the phorbol 12,13-dibutyrate-induced leakage of colloidal carbon. Pretreat ment with indomethacin (1 mu M) significantly increased colloidal carb on leakage in response to sapintoxin A, but did not affect the respons e to phorbol 12,13-dibutyrate. Increases in perfusion pressure caused by sapintoxin A (0.25 mu M) and phorbol 12,13-dibutyrate (1 mu M) were reduced by Ro 31-8220, but neither presser response was affected by i ndomethacin. Lower concentrations of phorbol 12,13-dibutyrate (0.25, 0 .1 mu M) had no effect on colloidal carbon leakage. However, there was a significant increase in perfusion pressure in response to 0.25 mu M but not to 0.1 mu M phorbol 12,13-dibutyrate. When rat mesentery alon e was perfused using gelatin-free physiological salt solution, sapinto xin A (1 mu M) had no effect on perfusion pressure, Whereas phorbol 12 ,13-dibutyrate (1 mu M) caused a significant increase over a 15-min pe riod, which was completely abolished by pretreatment with Ro 31-8220. It may be concluded that the permeability-increasing effects of phorbo l 12,13-dibutyrate are dependent on protein kinase C activation.