OVINE PROLACTIN INCREASES HEPATIC UCP-GLUCURONOSYLTRANSFERASE ACTIVITY IN OVARIECTOMIZED RATS

The potential role of prolactin in modulating hepatic UDP-glucuronosyl transferase (UGT) activity was studied. Ovariectomized adult female ra ts were treated with ovine prolactin (oPRL) at doses of 150, 200, 260 and 310 mu g/100 g b.wt. per day, for 4 days. Enzyme assays were perfo rmed in native and activated microsomes with p-nitrophenol as substrat e. Activation was achieved either by including UDP-N-acetylglucosamine in the incubation mixtures or by preincubating native microsomes with palmitoyl-lysophosphatidylcholine. Data obtained with UDP-N-acetylglu cosamine as activator showed that increasing doses of oPRL produced a progressive increase in enzyme activity up to a maximum of about 35% o ver basal values. Immunoblotting of microsomal protein with anti-UGT a ntiserum revealed also a dose-dependent increase in the immunoreactive protein. A kinetic method for measuring glucuronidating enzyme conten t confirmed the result of the immunoblot. oPRL induced minor changes i n the physicochemical properties of the microsomal membrane. Consisten t with this observation, studies performed with palmiloyl-lysophosphat idylcholine as activator showed no change in UGT latency, suggesting t hat the functional characteristics of the enzyme were not substantiall y affected by oPRL. The current data support the conclusion that prola ctin may act as a modulator of UGT activity by increasing the amount o f enzyme.