Alteration of normal development of drug metabolism by injection of growth hormone

Effect of hypophysectomy on caffeine elimination in rats

Two groups of 8-week-old Sprague-Dawley male rats were used: 8 hypophysectomized (H[-]), operated on day 0, treated by daily sc tetracosactid (ACTHs: 10 micrograms), and thyroxine (T4:5 micrograms/100 g); 7 sham-operated, treated by sc saline solution. ACTHs, T4, saline solution were administered on days 7-16. The animals received po caffeine (CAF) 4 mg/kg as citrate salt on day 15. Ten blood samples were drawn from the tail. Plasma CAF concentrations were determined by HPLC. CAF apparent clearance and apparent volume of distribution were lower in H(-) rats than in controls: 0.281 +/- 0.072 vs 0.455 +/- 0.165 l/kg/h (-38%; P less than 0.05) and 0.520 +/- 0.239 vs 1.28 +/- 0.266 l/kg (-59%; P less than 0.01) respectively. CAF half-life was lower in H(-) rats than in controls: 1.33 +/- 0.621 vs 2.12 +/- 0.676 h (-37%; P less than 0.01). CAF is a drug with a low hepatic extraction ratio and low plasma protein binding. CAF clearance is therefore primarily dependent on intrinsic clearance, which depends on the activity of the enzymes involved in CAF metabolism. These data suggest that hepatic CAF metabolism is reduced in H(-) rats treated by SC ACTHs and T4. The decrease in CAF apparent volume of distribution is probably related to dehydration, as suggested by increase in urine flow and hematocrit. The CAF half-life was probably low because the volume of distribution was proportionally more decreased than the clearance. Our results suggest that the pituitary gland plays a role in the regulation of hepatic CAF metabolizing enzymes.

Inducibility of the hepatic microsomal monooxygenase system experimentally reduced to a minimum amount/activity. Effect of hypophysectomy, partial hepatectomy and phenobarbital/toluene treatment on the hepatic polysubstrate monooxygenase system in rats

Sham-operated, hypophysectomized, partially hepatectomized and hypophysectomized + partially hepatectomized groups of CFY rats were treated with phenobarbital (40 mg/kg/day) per os or physiological saline once a day, or toluene-vapour (inhalation: 4,000 mg/m3, 8 h/day), for 3 days. The polysubstrate monooxygenase (PSMO) system of the liver was induced by phenobarbital after all kinds of surgical interventions. Inducibility of the enzyme system was the highest in the group with combined hypophysectomy + partial hepatectomy and decreased in order in the groups with partial hepatectomy, hypophysectomy and sham-operation. The relative cytochrome P-450 content (quantity of cytochrome P-450/100 g b.w.) was the lowest after combined operation, higher in partially hepatectomized and hypophysectomized animals and it was the highest in the sham-operated group. Hypophysectomy after partial hepatectomy seems to inhibit hepatic regeneration and to increase the inducibility of the enzyme by phenobarbital, at the same time. Phenobarbital treatment brought about SER proliferation in a part of liver cells, in each group. In case of repeated liver damage due to the consequences of hypophysectomy, partial hepatectomy, phenobarbital administration, a group of the liver cells responds to the first, another to the second, but even after the third injury a group of the liver cells maintained its regular structure. The hypothetical hepatotoxic effect of toluene, a widely used industrial solvent, has been tested. Hepatotoxicity has been excluded. The minimum non-specific hepatotoxic effect of the solvent was not augmented by either partial hepatectomy or hypophysectomy, or by the combination of the two. In all the experimental groups toluene increased the hepatic cytochrome P-450 level and induced a moderate increase in SER. Inducibility of the enzyme system after toluene inhalation was similar to that of the enzyme system after phenobarbital treatment in each group.

Perinatal development of cytochrome P-450, NADPH-cytochrome c reductase and ethoxycoumarin deethylase in rat liver nuclear membranes

Perinatal development of rat liver nuclear membrane enzymatic activities was investigated with respect to the metabolism of xenobiotica. The qualitative pattern observed was very close to that reported for microsomal enzymes during development. Cytochrome P-450, NADPH-cytochrome c reductase and ethoxycoumarin deethylase are already present in fetuses at 18 days of gestational age. Phenobarbital pretreatment appears to be effective as an inducing agent for all the enzymes studied, but only after birth. The pattern of induction of cytochrome P-450 showed a peak at the 38th day of life three times higher than basal values at that age. NADPH-cytochrome c reductase presented a constant elevation to about twice basal activity throughout the period taken into consideration. Ethoxycoumarin deethylase activity took only 17 days to reach the basal value observed later in adult animals. This enzyme proved highly inducible by phenobarbital (5-fold) early after birth but the increase dropped to 3-fold from the 24th day of life.

The time course of the effect of hypophysectomy and oestrogen treatment on the hepatic metabolism of androst-4-ene-3,17-dione in male and female rats

Hypophysectomy of male animals has little effect on the hepatic androst-4-ene,3,17-dione (androstenedione) metabolism, except for possible changes in the kinetics of the 16alpha-and 7alpha-hydroxylases. On the other hand, hypophysectomy of female animals leads to a "masculinization" of hepatic androstenedione metabolism, following the changes seen in Vmax. of the enzymes involved, probably due to the removal of the source of "feminizing factor" thought to maintain the "female" type of metabolism in the liver. There seems to be a temporal dissociation of the effects on the various enzymes, indicating different cellular control mechanisms for these enzymes. Oestrogen treatment of male rats causes "feminization" of the hepatic androstenedione metabolism. The time study shows an initial increase in 17-hydroxy steroid oxidoreductase and 6beta- and 16alpha-hydroxylase activities, followed by a decrease to the values in females. This biphasic effect is possibly due to an initial direct effect via the hypothalamo-pituitary system.