Resource partitioning during reproduction in the Norway rat

Rat pups nursed by pregnant dams grow as fast as pups reared by dams that are not pregnant. Moreover, litters that were in utero during a lactation are as numerous at birth and grow as fast as pups developing in a nonlactating, pregnant mother. These litters continue to grow as fast as pups born to nonlactating dams whether or not the first litter remains after the birth of the second litter. When pregnant and lactating dams have a restricted food supply, some dams are capable of extending the duration of their pregnancies by over 2 weeks past that of nonlactating, pregnant dams. This facultative prolongation of pregnancy apparently allows females to carry normal litters to term.

Protection against non-enzymatic deacylation of Met-tRNA Met m by the ribosome : an approach to the measurement of aminoacyl-tRNA : ribosome affinity constants

When bound to E. coli 70S ribosomes in the presence of poly (A, U, G) at 37 degrees C, Met-tRNA Met m is hydrolysed 20 times slower than when free in solution under the same conditions (lifetimes of 8.3 h and 22 min respectively). It is shown how this large difference in rate of hydrolysis may be used to study the equilibrium of aminoacyl-tRNA binding to ribosomes.

Evaluation of cardiac function in patients with thalassemia major

The application of noninvasive techniques to the evaluation of cardiac function in iron overload has identified a high incidence of abnormalities in asymptomatic patients prior to the onset of overt cardiac deterioration. Of the tests we have used, radionuclide cineangiography appears to be the most sensitive because it can be conveniently applied during the physiological stress of exercise. Other tests of cardiac function that include stress are also likely to be more sensitive than resting measurements of cardiac function. Systematic application of these techniques to the study of patients on iron chelation therapy should results in an early determination of the efficacy of such treatment.

Acute elevation of the heat load of mother rats curtails maternal nest bouts

Elevation of the rate of rise of ventral, core, or preoptic area temperature in mother rats while they were nesting with their offspring curtailed nest-bout durating. In addition, the naturally occurring curtailment of nest bouts that occurs in mothers caring for large pups was found to be accompanied by an elevated rate at which maternal temperature rose over the course of a nest bout. These data are consistent with the suggestion that nest-bout duration is thermally limited.

Thermoendocrine influences on maternal nesting behavior in rats

Adrenalectomy-ovariectomy (adex-ovex) of mother rats resulted in prolonged nest bouts with their young. Glucocorticoid, but not progesterone or aldosterone, replacement therapy to adex-ovex dams limited the duration of maternal nesting bouts by successfully restoring the chronic vulnerability of these mother rats to the acute thermal consequences of huddling with the young. This vulnerability appeared to be due to a chronic elevation of maternal temperature. When the heat load of hormone-disrupted mothers was chronically elevated, the dams were subject to an acute rise in temperature while huddling with their young, and nest bouts were curtailed.

Autoradiography of technetium-labelled diphosphonate in rat bone

The passage of technetium-labelled methylene diphosphonate (99mTc-MDP) across rat bone was examined by autoradiography. The autoradiographs showed that shortly after an injection of the bone-seeking agent there was activity outside the bone, within the bone marrow and also adjacent to the highly vascular epiphysial plate; the distribution of the isotope in the incubated bone appeared to be non-uniform, a high concentration being seen adjacent to the epiphysial plate and also on the surfaces of the bone. The evidence suggested that a two-fold mechanism resulted in the uneven distribution of 99mTc-MDP. The first factor probably represented the regional distribution of blood flow with a transcapillary movement of the tracer from the capillary bed to the extravascular space; the subsequent incorporation of the tracer into bone appeared to depend on the nature of the bone matrix.

Maternal behavior in the rat: facilitation through gonadectomy

Virgin rats were ovariectomized and tested for induction of maternal behavior by being housed with neonatal young. A postoperative interval of 8 weeks yielded an average latency for the onset of maternal behavior significantly lower than that for intact controls or for virgin females ovariectomized 4 weeks before testing. Replacement of estrogen in the group ovariectomized for 8 weeks or injection of the estrogen antagonist ethamoxytriphetol (MER-25) in the group ovariectomized for 4 weeks changed the average latencies accordingly. Parallel results were obtained for males that were castrated 4 or 8 weeks before testing. It is concluded (i) that maternal behavior is under gonadal control and that this control is normally inhibitory; and (ii) that only after long-term removal of the gonads, resulting presumably in the complete clearance of estrogen and testosterone, is the maternal mediating system finally released from steroid suppression.

Prolactin in the postpartum rat: synthesis and release in the absence of suckling stimulation

Postpartum female rats deprived of suckling stimulation while being kept continuously with pups nonetheless suspended ovarian cyclicity for an average of 16 days and responded to uterine trauma by forming deciduomata. These results show that the extramammary stimulation afforded by young is alone capable of sustaining prolactin output from the adenohypophysis of the postpartum rat.