Effects of steroid hormones on total brain Na⁺-K⁺ ATPase activity in <i>Oreochromis mossambicus</i>

Abstract

The effects of administration of cortisol, corticosterone, testosterone, progesterone and a synthetic estrogen, diethylstilbestrol (DES) on total brain Na⁺- K⁺- ATPase were investigated in tilapia, <i>O</i>. <i>mossambicus. </i>Exogenous administration of 0.125 and 0.25μ<i>g/ </i>g body weight of glucocorticoids and 0.125, 0.25 and 0.5<i>μg/ </i>g body weight of DES for 5 days significantly stimulated Na⁺- K⁺ ATPase activity by 14-41% in the brain, while 0.5<i>μ</i>g<i>/ </i>g body weight of glucocorticoids did not evoke any response on the activity of the enzyme. Progesterone (0.125 and 0.25<i>μ</i>g<i>/ </i>g body weight) administration significantly decreased the enzyme activity by 21-36% and high dose (0.5<i>μg/ </i>g body weight) was ineffective. Testosterone exhibited a biphasic effect on Na⁺-K⁺ ATPase activity - a low dose stimulated by 14% while middle and high doses inhibited it by 19-24%. The results seem to be the first report on the effect of steroids on brain ATPase activity in a teleost. When 0.25<i>μg/ </i>g body weight of actinomycin D or puromycin was administered prior to the treatment of similar doses of hormones, the inhibitors significantly inhibited the effect of the hormones by 24-52 %. This clearly shows that the effect of the hormones was sensitive to the action of inhibitors suggesting a possible genomic mode of action under long term treatment. The results suggest that cortisol, corticosterone and DES may possibly stimulate the co-transport of glucose and excitation of membrane potential while progesterone and testosterone inhibit them in the brain of <i>O</i>. <i>mossambicus </i>by regulating the activity of Na⁺-K+ ATPase.