Maurice A. Robkin

Autonomic receptors of the early rat embryo heart growth and development.

The adult heart rate responds to stimulation of the sympathetic and parasympathetic nervous system. These responses are mediated by the release of norepinephrine and acetylcholine (ACh) which act on beta-adre-nergic and on muscarinic-cholinergic receptors, respectively. During rat embryogene-sis, the heart commences to beat during Day 10 and circulation is established before these nerves reach and innervate the heart on Day 15 (1-3). The effect of ACh on the beat rate of excised rat embryo hearts has been reported by two groups of workers and their conclusions differed; Hall (4) observed a decrease in rate in the Day 11 ½ and older embryos but Pager et al. (5) could not demonstrate this effect until Day 16½. Our studies using the whole explanted embryo suggest an explanation for this discrepancy. Cholinergic receptors can be experimentally distinguished into two types by (a) their response to atropine, which selectively blocks muscarinic receptors, and (b) to curare, which selectively blocks nicotinic receptors. The experiments reported in this paper demonstrate the presence of cholinergic receptors in the preinnervated intact embryonic heart, consistent with Halls result in the excised heart, classify them as being of the muscarinic type and show that they are independent of the adrenergic receptors in their action and time of functional appearance. We have found (6) in the explanted whole embryo that the adrenergic response of the heart appears during Day 10 concom-mitant with the onset of heart function, a result similar to that of Halls with excised hearts. Our findings indicate that cholinergic response first appears approximately ½ day later in development than the adrenergic response, a finding also first observed by Hall. Methods. Embryos were explanted at either Day 10 1/2 (10–15 somites) or Day 11 (21-26 somites) of gestation. The explantation procedure followed was as described in New (7), Shepard et al. (8), and Robkin et al. (9).

In vitro culture of somite stage rat embryos: A new technique for maintaining growth and continuously monitoring heart rate: Applications in metabolic and teratologic studies

SummaryRat embryos removed during somite stages were attached to small rafts by using the technique described by D. A. T. New (J. Embryol. Exp. Morphol. 17: 513–525, 1967). The embryos were maintained in a viable growing state in circulating human serum. Twenty-four-hour cultures of day 11 rat embryos resulted in nearly normal increases in somite count, but length and protein increments were about one-half of in vivo values. After 24 hr of culture, the embryos were generally translucent and showed no apparent areas of gross or microscopic tissue necrosis. The apparatus is extremely compact and requires only about 9 ml of medium, which is sufficient to support three embryos. The small volume allows measurement of metabolites consumed or liberated with reasonable accuracy. By use of a technique of transillumination, using a laser and photomultiplying tube, a detailed and continuous record of heart rate can be made. Addition of drugs to, and sampling of, the culture medium is done easily.With this technique, a linear dependence of heart rate on temperature between 30 and 40°C has been shown. Studies of energy metabolism indicated that the earliest stage studied (about 11 somites) was characterized by a relatively high glucose utilization rate, with the major end product appearing as lactate. Further evidence that this stage was functioning anaerobically was shown by the presence of a resistance to aerobiosis. Embryos with 25 or more somites utilized less glucose, produced less lactate, and were damaged by lack of oxygen.

Estimated maximum thyroid doses from 129I releases from the Hanford site for the years 1944-1995

129I, a very long lived fission product, persisted in the environment after discharge from the chemical reprocessing plants at Hanford. The significance to human health is evaluated by considering the maximum possible impact it might have. Allowing the total production of 129I to be discharged to the air and considering the location where the maximally exposed individuals residue, the lifetime cumulative thyroid dose is calculated as a function of birth year. The maximally exposed individual at the maximum exposure location was born in 1954 and accumulates a thyroid dose between 1954 and 1995 of slightly over 9,000 microSv (900 mrem) at an average rate of 220 microSv (22 mrem) y-1. Over the same period of time, the soft tissue dose from background radiation due to both external and internal radiation is about 38,000 microSv (3,800 mRem).

A simplified model for estimating health effects due to leaching of long-lived nuclides stored in a radioactive waste repository.

Evaluation of alternate methods of treating long-lived radionuclides to be stored in a waste repository include evaluating the differences in health effects from a potential release due to the distribution of nuclides produced by each method. The potential for release and the health effects extend into the indefinite future so predictions of human behavior become speculative. A simple model is proposed which incorporates the nuclides in the repository, leached, in transit in ground water, discharged to surface water, used for irrigation, taken up into crops and ingested. The model yields a solution of simple form and permits the evaluation of potential health effects per unit activity of a nuclide initially placed in the repository. The model is applied to calculate the potential health effects due to the nuclides occurring in a 4n, 4n + 1, 4n + 2, and 4n + 3 decay chain.