EXPERIMENTAL STUDY OF THE CONTROLLED HYPOTENSIVE EFFECT OF LAbETALOL Hcl AND ITS POSSIBLE SKELETal MUSCLE REIAXANT EFFECT
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Labetalo1 infusion is becoming more commonly used in controlling the blood pressure during anaesthesia in different situation. This work was designed to study the controlled hypotensive effect of labetalol infusion. with any possible effect on the skeletal muscle. It was found that labetalot infusion (100 tig /kglminute) produced a gradual reduction of the systolic blood pressure from110 + 8 to 70 + 6 mm Hg and the diastolic blood pressure from 100 + 8 to 60 + 6 mm Hg. This hypotensive effect was mentamed during the infusion of labetalol. After stoppage of infusion the blood pressure and the H. R returned within 20 min. to their normal levels. Also, it was observed that labetalol infusion attenuated the vasopressor effects of phenylepherine (1 ug / kg), adrenaline (1 ug /kg) and abolished completely the hypotensive effect of isoprenaline (0.5 ug/ kg). Moreover, during labetalol infusion, there was 20 % reduction in the contraction of gasterocnemius of cats. This reduction was not reversed by stoppage of infusion but it was reversed by L V. infusion of neostigmine (100 ug /kg). In addition, it was observed that the relaxant effect of DTC. was potentiated during labetalol infusion and this effect was reversed only by neostigmine (100 ug / kg). The in-vitro results revealed that labetalol in concentrations of 0.2, 0.4, 0.8, and 3.2 ug / rrareduced the indirect and direct contractions of rat phrenic nerve diaphragmpAch and kcl induced contractions of isolated rectus abdominis muscle of toad in dose dependent manner Accordingly the skeletal muscle relaxant effect of labetalol should be investigated clinically and put it in consideration during its use for controlling blood pressure.