The effects of thyroparathyroidectomy and 1,25 dihydroxyvitamin D3 on changes in the activities of some cytoplasmic and nuclear protein kinases during liver regeneration

Abstract

Partial hepatectomy (HPX), which proliferatively activates the remaining liver cells, triggered two transient prereplicative surges in the total activities of cytoplasmic types I and II cyclic AMP‐dependent protein kinase holoenzymes, and of nuclear catalytic subunits from cyclic AMP‐dependent protein kinases. It also induced a transient prereplicative increase in the activities of a nuclear Ca²⁺‐calmodulin‐stimulable, protamine‐phosphorylating protein kinase, and a nuclear poly(L‐lysine)‐phosphorylating, 105 kDa protein kinase. Thyroparathyroidectomy (TPTX) delayed and reduced the first surge and completely eliminated the second surge of both of the cytoplasmic cyclic AMP‐dependent protein kinases, reduced the rises in the activity of nuclear catalytic subunits, and completely eliminated the surge of the Ca²⁺‐calmodulin‐stimulable protein kinase, but did not affect the surge of the nuclear 105 kDa protein kinase. The impairment of the responses of the two cyclic AMP‐dependent protein kinases to HPX in TPTX rats was not accompanied by a rise in the level of heat‐stable inhibitor of cyclic AMP‐dependent protein kinase activity. One intraperitoneal injection of 1,25‐dihydroxyvitamin D₃ into TPTX rats immediately after HPX completely restored the post‐HPX surges in the activity of type I cyclic AMP‐dependent protein kinase, but the hormone, even in high doses, had little or no effect on the type II isoenzyme or the nuclear Ca²⁺‐calmodulin‐stimulable, protamine‐phosphorylating enzyme.