Effects of background adaptation, length of exposure time and hypophysectomy on the quantity of melanophore-stimulating substances in the hypothalamo-hypophyseal complex of Rana pipiens

Abstract

The quantity of the individual melanophore-stimulating substances (MSS's) was determined in aqueous extracts of the pars intermedia (PI), pars distalis (PD), and hypothalamus (H) of frogs which were light (L) or dark (D) adapted (A) for 2 or 8 days. The quantity of two of the substances common to the PI and PD was greater in LA than in DA frogs. In fact, one of the MSS's of the PI was not detectable in DA frogs. With the exception of the MSS which was not detectable, more MSS was present in the PI at day 8 than at day 2 for both DA and LA frogs. One MSS of the PD increased in quantily by day 8 when the frogs were light adapted, but did not increase in quantity after 8 days of dark adaptation. The second MSS of the PD was greater in quantity at day 8 than at day 2 in both DA and LA frogs. In both the PI and PD, the third MSS did not vary with background or length of exposure. The quantity of the single MSS in the H was greater in DA than LA frogs. There was more MSS in the H at day 8 than at day 2 in DA frogs, but in LA frogs the quantity did not change with length of exposure, nor was the MSS depleted. Hypophysectomy of frogs DA for 8 days reduced the quantity of MSS in the H to a level not significantly different from the level in LA frogs after 8 days of exposure. In conclusion, two of three MSS's of the PI and of the PD fluctuated in response to changes in background coloration and to the length of background exposure. The reduction in H content of MSS after hypophysectomy of dark-adapted frogs indicates that the major portion of H MSS originates in the hypophysis.