Porcine anterior pituitary

Quantitative Relationship of Agonist and Antagonist Ligand Binding to Porcine Anterior Pituitary Gland Membranes... 

Porcine anterior pituitary membranes were incubated with increasing concentrations (10 pM-900 pM) of [sHjn-propylapomorphine in the presence of 10 / M and 1 mM GTP and in the absence of GTP as the control. Nonspecific binding was determined in the presence of 1 mM (+)butaclamol and was the same with or without the addition of GTP. Data were analyzed as described in Figure 1. The number of sites labelled by [3H]n-propylapomorphine was 26.7 pM (absence), 19.6 pM in the presence of 10 / M GTP and 6.0 pM in the presence of 1 mM GTP and dissociation constants for the ligand were 280 and 210 pM. The experiment was performed in duplicate and is representative of three such experiments. 

All the data presented above point to the involvement of a putative guanine nucleotide binding protein in the interaction of agonists with the dopamine receptor in the porcine anterior pituitary gland. We, therefore, wanted to obtain more compelling evidence for the interaction of a nucleotide binding... 

Porcine anterior pituitary membranes were incubated as described in Figure 1 with [3HJspiro-peridol (10-1100 pM). Nonspecific binding was determined in the presence of 1 mM (- -)buta-clamol. Data were analyzed by curve fitting with a model for the binding of the radioligand to one or two classes of sites (14). Data are presented in the Scatchard plot coordinates. The experiment was performed in duplicate and is similar to several other experiments with the same results but it represents an extreme case of the ability of the [3H] antagonist to discriminate between the two forms of the receptor. The two dissociation constants calculated for the control curve are different by about 10-fold. (Reproduced with permission from Ref. 25. 

GRF has been isolated and characterized from a human tumor of the pancreas (61) as well as from rat (62), porcine (63), bovine (64), caprine (65), ovine (65), and human (65) hypothalamus stalk-median eminence. It is a 40-44-amino-acid peptide hormone produced in the arcuate nucleus of the hypothalamus and released from neurosecretory nerve terminals of these arcuate neurons, and it is carried by the hypothalamo-hypophysial portal circulation to the anterior pituitary gland where it stimulates growth hormone (GH) secretion (66). 

Extracts of the intermediate-posterior lobe of the mouse pituitary contain approximately a tenth as much ACTH activity as extracts the anterior lobe (Mains and Eipper 1975). In extracts of both the anterior and the intermediate-posterior lobes, about half of the immunological ACTH activity is similar in size to porcine ACTH (Mr = 4000-5500). Two higher M, forms of ACTH account for the remainder of the ACTH activity. About 40 % of the immunological ACTH activity in anterior lobe extracts has a Mr of 6500-9000. Extracts of both the anterior lobe and the intermediate-posterior lobe contain ACTH activity with a Mr of 20,00-30,000. 

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