Nature of moulting control in amphibians: effects of cortisol implants in toads Bufo bufo

Implantation of cortisol pellets in a dorsal lymph sac reduced the frequency with which toads replaced the strata cornea of the epidermis. Except in a few cases, however, the replaced strata cornea were not shed as in a normal moult. The mean interval between replacements of strata cornea rose from about 9-10 days in control toads to about 18 days in intact toads bearing implants. Removal of the cortisol pellets approximately 1 month after their insertion was followed by moulting on the fourth (or fifth) day. After the first moult, the frequency of replacement of strata cornea was initially high, but returned gradually to the normal level, probably concurrently with increasing levels of endogenous adrenocortical hormones. In toads with extirpated or ectopically transplanted pars distalis of the hypophysis, implanted cortisol pellets increased the interval between replacements of strata cornea from some few days to about 14-15 days, not significantly different from the intact toads, but no sheddings occurred. It is concluded that the moulting rhythm in toads, and other amphibians, is basically a rhythm in epidermal differentiation, expressed in the frequency with which the strata cornea are being replaced. The duration of the intervals between replacements varies with the level of circulating hormones, and replacement proceeds in the absence of a corresponding rhythm in secretion of the hormones. Shedding of a replaced stratum corneum depends upon the integrated function of a complex of processes, susceptible to disruption. Such disruption presumably prevailed at the pharmacological levels of circulating hormone in the cortisol-implanted toads.