The binding of [3H]physalaemin [( 3H]PHY) to rat brain membranes is specific, saturable and reversible in the presence of monovalent cations and peptidase inhibitors. Monovalent cations increase the binding of [3H]PHY in an ionic strength (mu)-dependent manner with an optimal effect at mu higher than 0.3. Addition of 2.5 mM MnCl2 results in a 2-fold increase in the affinity (KD) and a 40% increase in the maximal receptor density (Bmax). Scatchard analysis under these conditions indicates the existence of a single population of noninteracting sites with KD of 3.6 nM and a Bmax of 76 fmol/mg of protein. Substance P (SP) and physalaemin are equipotent in inhibiting the binding of [3H]PHY, whereas the potency of SP(2-11), SP(3-11), and SP(4-11) decreased in inverse proportion to their length. The relative affinity of the different tachykinins, SP, and SP fragments in competing with [3H]PHY correlates with their potency to stimulate several bioassay systems, indicating that [3H]PHY labels a physiologically relevant binding site that correspond to the SP-P tachykinin receptor. Guanine nucleotides completely abolish the increase in the binding of [3H]PHY produced by 2.5 mM MnCl2, but in its absence, the nucleotides reduce binding only by 15%. Guanine nucleotides reduce binding to the same level regardless of the presence or absence of the divalent cation. Regional distribution studies confirm that the density of SP receptors is maximal in the olfactory bulb, followed by the hypothalamus, striatum, hippocampus, cortex, and cerebellum.
Effects of LH and prolactin on cultures of granulosa cells from the goat were analysed in terms of the secretion of progesterone. The cultures were maintained for 120 h during which time they were treated at 24 and 72 h after explantation with LH and prolactin. Progesterone secreted in the culture medium was determined by radioimmunoassay. The secretion of progesterone by the cultures in response to LH and prolactin was significantly increased (P less than 0.01) compared with that by control cultures. The pattern of steroid secretion in the two cases (LH-treated and prolactin-treated cultures) was, however, different. The secretion dropped appreciably when the concentration of hormones was increased to 100 mu./ml.
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