Effect of colchicine on the uptake of prolactin and insulin into Golgi fractions of rat liver.

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Abstract
125I-labeled prolactin is taken up by a receptor-dependent process and concentrated in an intact form in Golgi elements from female rat liver. The effect of colchicine on this uptake process into Golgi elements is examined. Colchicine [25 .mu.mol (10 mg)/100 gm body wt] was injected i.p. in adult female rats, and hepatic Golgi fractions were prepared at 1, 2 and 3 h postinjection. The enzyme recoveries and morphological appearance of fractions from colchicine there was a marked (> 60%) inhibition of uptake of 125I-ovine prolactin (125I-oPRL) into Golgi light and intermediate fractions but no inhibition of uptake into Golgi heavy and plasmalemma elements. Intermittently, from 2-45 min postinjection, 125I-oPRL was extracted from Golgi elements and found to be largely intact as judged by rebinding to receptors. The inhibitory effect of cholchicine was seen at doses ranging from 0.25-25 .mu.mol/100 g body wt. Vincristine also inhibited 125I-oPRL uptake into the Golgi light and intermediate fractions but lumicolchicine had no inhibitory effect. There was a smaller effect of colchicine at early (1 h) and later (3 h) times on the extent and pattern of 125I-insulin uptake. Colchicine treatment did not produce a significant change in lactogen receptor levels in the Golgi fractions. Colchicine treatment inhibited the transfer of prolactin into Golgi vesicular elements. The much smaller effect on insulin uptake suggests that there may be differences in the manner in which the 2 hormones are handled in the course of internalization.