Quantitation of LH subunits released by rat anterior pituitary cells in primary culture

Immunoreactive rLH, rLHα, rLHβ and rFSH in the cell extracts and medium of rat anterior pituitary cell cultures were measured after gel filtration on Sephadex G-100 Superfine. Cell extracts contained uncombined rLHα and rLHβ present as approximately 40% and 4%, respectively, of native rLH on a molar basis. Unstimulated cultures appeared to release a large excess of rLHβ ( $ ̃2560% of rLH on a molar basis) as well as a minimum of uncombined rLHβ. Stimulation of cultures with physiological (LHRH) or non-physiological agents (A23187, elevated K⁺) increased the absolute but not the relative quantities of uncombined subunits released relative to those present intracellularly. Thus, rat anterior pituitary cell cultures appear to produce and release an excess of free a subunit as well as a minimum of uncombined rLHβ. However, one cannot be certain whether the uncombined rLHβ represents a pool of 'free' rLHβ or simply results from the dissociation of rLH.