Abstract
The protein synthetic activities of membrane-bound and free hepatic ribosomes isolated
from intact rats fed ad libitum, and normal rats subjected to food restriction to
match that of hypophysectomised (Hx) rats were compared to the in vitro protein synthetic
capacity of hepatic ribosomes isolated from Hx rats.
Hypophysectomy resulted in decreased protein synthetic ability of bound ribosomes,
whether protein synthesis was directed by endogenous messenger RNA (mRNA) (p < 0.05)
or by polyuridylic acid (polyU) (p < 0.01). In contrast, the protein synthetic activity
of free hepatic ribosomes from Hx rats was reduced when protein synthesis was directed
by endogenous mRNA (p < 0.05) but, when polyU was substituted as the messenger, the
protein synthetic activity of these free ribosomes was equal to that of control rats.
On the other hand the effects of food restriction on hepatic ribosomal function could
be clearly differentiated from the effects observed following hypophysectomy. Thus,
the reduced protein synthetic activity of hepatic bound ribosomes isolated from food
restricted normal rats was not demonstrable, when polyU was used to direct protein
synthesis. Further, food restriction had no effect on the protein synthetic activity
of free hepatic ribosomes, and this was true when protein synthesis was directed by
either endogenous or artificial messenger. It is concluded that hypophysectomy reduces
the protein synthetic ability of both bound and free hepatic ribosomes, and this change
of ribosomal function of Hx rats cannot be attributed to their decreased food intake.
Key words
Hepatic, Bound and Free Ribosomes - Hypophysectomy - Food Deprivation - Protein Synthesis
1 Present address: Department of Medicine and Endocrine Unit, St. Vincent's Hospital,
Victoria Parade, Fitzroy, Victoria, Australia
