Diabetes was produced by withholding insulin treatment from previously alloxanized female rats. Isometric contraction was assessed in soleus and extensor digitorum longus (EDL) muscles removed 2 h to 32 days after insulin withdrawal. Directly induced contractions were measured in vitro at 20 degrees C. In soleus muscles from severely diabetic rats, average twitch and tetanic forces were normal or slightly greater than that of controls of similar age, whereas in EDL, marked decreases appeared in both twitch and tetanic forces. Soleus muscle from severely diabetic rats was not depolarized as already reported in EDL. After 16 and 32 days in the diabetic state, soleus muscles from moderately diabetic rats generated average tetanic forces that were equal to that found in age-matched controls, whereas EDL tetanic forces were significantly (P = less than 0.01) weaker. Average specific twitch force in diabetic soleus muscles was greater than age-matched controls after 16 and 32 days in the diabetic state. In diabetic soleus muscle, significant increases in the average half relaxation time and twitch duration were seen after prolonged (16 and 32 days) periods of diabetes. No changes were seen in the same temporal parameters of the twitch in diabetic EDL muscle. A greater atrophy appeared in EDL than in soleus after 16 and 32 days of uncontrolled diabetes.

Internal pH (pHi) was analyzed in rat extensor digitorum longus (Edl) muscle at 30 degrees C with single-barrel liquid ion-selective electrodes. Average pHi in 284 cells was 7.197 +/- 0.006. Increases in CO2 from nominally 0 to 5% produced an acidification from which recovery took place. In different groups of cells, recovery from the 5% CO2 acidification was significantly inhibited by 100 microM 4,4' diisothiocyanatostilbene 2,2' disulfonic acid (DIDS), Cl removal, Na removal and 2 mM amiloride. Prepulsing with 20 mM NH4 in the presence of CO2/HCO3 typically reduced pHi to only about neutral, whereas 50 mM reduced pHi to 6.7-6.8. In the nominal absence of CO2/HCO3, 20 mM NH4 reduced pHi to about 6.7 from which recovery took place at about 58% of the rate seen in different cells in the presence of CO2/HCO3. In the presence of CO2/HCO3, cells prepulsed with 50 mM NH4 had fully recovered to an average pHi of 7.22 +/- 0.04 about 90 min after removal of NH4. However, 90 min after removal of 20 mM NH4 in the absence of CO2/HCO3, average pHi was significantly less (7.05 +/- 0.03). Intrinsic buffering capacity (beta i) was obtained during pulses of CO2, acetic acid or after an NH4 pulse. beta i was significantly reduced in the absence of HCO3, Cl or Na and HCO3. The data provide significant support for an important role of HCO3 in the control of pHi in fast-twitch muscle.

Diabetes mellitus was produced by withholding insulin from female rats previously treated with alloxan. In vitro studies of contractile and electrical properties of the extensor digitorum longus muscle were analyzed at various periods following cessation of insulin treatment. In severely diabetic ketoacidotic rat muscles it was observed that both direct and indirectly induced twitch and tetanic tensions were significantly reduced to the same degree. Resting membrane potentials were significantly reduced but repolarized when external chloride was removed. Indirectly induced action potential amplitude and rate of depolarization were significantly depressed and there was a significant increase in action potential duration. Specific membrane in action potential duration. Specific membrane resistance decreased significantly but transiently due largely to an increase in chloride conductance and specific capacitance increased significantly. After extended periods of milder diabetes, specific tetanic tension decreased slightly while specific twitch tension was unchanged in both direct and indirectly induced contractions. Resting potentials were only slightly reduced. Indirectly elicited action potential amplitude and rate of depolarization were slightly reduced. Specific membrane resistance was significantly increased largely due to decreases in chloride conductance. Specific capacitance was unchanged.

Until recently studies of changes in thyroid gland function as a result of various degrees of food restriction were based upon morphological evidence ( 1 ) , studies of altered 1131 uptake ( 2 ) , and upon thyrotropin content of blood(3). With availability of a direct method of estimating thyroxine secretion rate (TSR)(4) it is possible to obtain quantitative data on influence of various degrees of food restriction on TSR.In studies of factors influencing TSR it is important to be able to differentiate the effect of experimental procedure per se and restriction of food consumption which may be associated with experimental conditions or endocrine gland removal. Reduction in TSR in mice associated with degrees of feed restriction has been reported(5). The present paper reports upon effect of feed restriction upon TSR of rats.Materials and methods. Mature female Sprague-Dawley-Rolfsmeyer rats weighing approximately 250 g were maintained at temperature of 78 L -1°F with artificial lighting provided during daylight hours. Control TSR values were determined while animals were on ad Zibitum diet. TSR determinations were repeated beginning 3 and 17 days after initiation of food restriction in each animal. The end-point of each determination required up to 12 days. Animals in lower TSR range reached end-point earlier than in higher range and were restricted for a shorter period. Each animal received 2 pc carrier free 1131 and was allowed 48 hrs for uptake. Counts were made at 48-hr intervals and thyroxine (T4) dosage was begun at 0.25 pg/lOO g BW and without blockage of thyroidal 1131 release (95% previous dose) increased by 0.25 pg at every counting interval. Purina Lab Chow in granular form was weighed out daily according to individual initial weights of animals. An 8, *Contribution from Mo. Agr. Exp. Sta. Journal t This investigation was supported in part by a Series No. 2427. Approved by Director. grant from U. S. Atomic Energy Commission.17, 22 and 48% reduction from the normal mean value of 5.26 g/100 g BW was given to each animal(6). Body weights were taken on alternate days.Results. Reduction of food intake depressed TSR depending on degree of food restriction in almost every case (Table I). During the first interval (3-14 days), an 8% reduction in food intake had no effect on TSR as shown by a non-significant increase in TSR (t = 0.274). Reductions in food intake of 17% resulted in an 8% reduction of TSR as compared to control value. A 2276 food reduction depressed TSR by 13%. These reductions are non-significant. However, a reduction of 48% resulted in a 2870 depression of TSR which was significant (t = 2.3).During second interval of food restriction ( 17 to 2 7 days) , more profound reductions in TSR were apparent. A 23% reduction in TSR occurred with an 8% reduction of food intake during this period. When food intake was reduced 1770, TSR was depressed by 15%. Statistically, these reductions in TSR are not significant. A 22% reduction of food results in a significant (t = 2.445) 42% depression in TSR while a ...

In the absence of external HCO3, resting membrane potentials (Vm) in extensor digitorum longus muscle were depolarized as compared to the normal Vm in the presence of HCO3. Removal of Na or Cl form the HCO3-free media induced repolarization. In muscle in HCO3 buffer at 20 degrees C, internal K, Na, and Cl activities were analyzed with liquid ion selective microelectrodes. The averages were respectively, 119.7 +/- 2.1, 6.69 +/- 0.3, and 3.41 +/- 0.06 mM. In a high proportion of cells analyzed, the equilibrium potential for Cl was negative to Vm. Removing external HCO3, decreased internal K while internal Na and Cl increased. An increase in temperature and the application of HCO3 significantly lowered internal activities of both Na and Cl. Removal of HCO3 with temperature held constant caused a rapid depolarization, an increase in internal Na and Cl, and a decrease in internal K. Furosemide (10 microM) induced a repolarization of cells that were previously depolarized in the HCO3-free state, but the drug does not decrease internal Na.