Dynamics of adenylate cyclase desensitization during long-term exposure to the hormone

The dependence of adrenal gland adenylate cyclase desensitization on the dose of in vivo injected ACTH, the time of occurrence and duration of the enzyme refractory period and the dependence of desensitization on the number of ACTH injections were analyzed. The experiments were carried out on guinea pigs injected with prolonged action preparations of ACTH (4 and 6 units) daily for 1-6 days. Intramuscular injections of ACTH caused adenylate cyclase refraction to the repeated action of the hormone. The effect of desensitization was the most conspicuous within the first few hours after hormone injection. The decrease of adenylate cyclase sensitivity and the duration of this effect were found to depend on the ACTH dose as well as on the number of injections. It has been shown for the first time that a single in vivo injection of 0.9% NaCl causes short-term desensitization of adenylate cyclase to the repeated action of much higher doses of ACTH in vitro, presumably due to endogenous ACTH release in response to weak stress exposure. The periodicity of changes in adenylate cyclase sensitivity upon prolonged hormone administration is discussed. Sensitization of the enzyme upon daily short-term exposure to physiological doses of ACTH (administration of 0.9% NaCl for 6 days) was revealed.     

Seasonal Changes of the Metabolites in the Leaves, Bark and Xylem Tissues of Olive Tree (Olea europaea. L) II. Carbohydrates

Seasonal changes of starch and soluble carbohydrates in leaves,bark and xylem tissues of olive tree were examined during acomplete annual cycle. Leaf starch and soluble carbohydrateswere detected at high levels during the spring and autumn metabolicallyactive periods. The low level of leaf starch in combinationwith the drastic reduction of soluble carbohydrates and mannitol,defined the summer period of the low metabolic state of thetree. The low leaf starch level in conjunction with the risensoluble carbohydrate levels in leaves in winter were associatedwith cold acclimation processes. The bark and xylem tissueswere performing as starch deposition sites, and differencesin the extent of starch accumulation in these tissues were detectedduring the seasons. The starch fluctuations in bark and xylemwere discussed in relation to the translocation of metabolitesand other physiological processes. Mannitol, the most abundantleaf carbohydrate, was examined in relation to the reducingsugars exported to the bark. The bark mannitol was examinedin conjunction with the sucrose, glucose and starch levels inthe maturing bark tissues and was correlated to the low wintertemperatures. During the winter there was a drastic reductionof mannitol circulation from the bark to xylem. Olive tree, Olea europaea, L, carbohydrates     

Polarizing activity in the developing limb of the Syrian hamster.

The transplantation of small pieces of tissue from the limb buds of 9 1/2 -10 day hamster embryos to the wing bud of the chick results in the induction of supernumerary wing structures. The anteroposterior polarity of these induced structures is under the control of the transplanted hamster tissue. The developing hamster limb thus has limb polarizing activity similar to that found in avian species and, as in the chick, the activity is found primarily in the posterior region of the limb bud.