Administration of PMSG to 26-day-old rats did not increase the total number (non-atretic and atretic) of preantral (Type 4) and antral (Types 5 and 6) follicles but changed the proportion between non-atretic and atretic follicles. By 12 h after PMSG administration only 7% of Type 5 follicles were atretic, and no atretic follicles of Type 6 were observed, as compared to 52 and 62% atretic follicles, respectively, in the saline-treated controls. PMSG did not decrease the percentage of atresia in preantral (Type 4) follicles. The treatment was associated with a sharp fall by 12 h in the pyknotic index of antral (Types 5 and 6) follicles. It is concluded that PMSG causes superovulation in the rat by rescuing follicles of Types 5 and 6 from atresia and allowing them to reach ovulation.

Summary. Graafian follicles from rats treated for 1 or 2 days with pentobarbitone sodium (Nembutal)

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This paper describes properties of 86Rb fluxes through K channels in "luminal" membrane vesicles prepared from rabbit renal outer medulla. By measuring 86Rb uptake against an opposing chemical gradient of K ions, using membranes loaded with KCl, a transient accumulation of isotope is observed, which is blocked by Ba ions. This is the behavior expected of a conductive Rb flux through a Ba-sensitive K channel. The 86Rb accumulation is driven by an electrical diffusion potential as shown in experiments using either vesicles loaded with different anions, or an outwardly directed Li gradient with a Li ionophore. The vesicles containing the channel show a cation selectivity with the order Rb greater than K greater than Cs greater than Li greater than Na greater than choline. The Ba-sensitive Rb flux is dependent on Ca within the vesicles, with a very high affinity estimated as K0.5 10 to 100 nM. The vesicles appear to be right-side-out. The Ba-sensitive 86Rb uptake is also inhibited by quinine K0.5 30 microM but is insensitive to tetraethyl ammonium ions and apamin. These isotope flux experiments complement electrophysiological experiments in providing independent evidence for the existence of K channels in the luminal surface of cells of this ascending limb of the loop of Henle. The very high Ca affinity suggests that cytoplasmic Ca could play an important role in regulation of transepithelial salt flux in this region of the nephron.