Differences between pregnant and nulliparous rats in basal and stress levels of metallothionein

Effects of restraint stress in gestation: implications for rodent developmental toxicology studies

Restraint has been used as a procedure to study the effects of stress on gestation outcome in rodents. The effects of restraint could potentially be used as a model for the impact of general stress produced by high doses of toxicants and other interventions. In mice, restraint in the peri-implantation period leads to implantation failure, and restraint at appropriate times in organogenesis produces cleft palate, supernumerary ribs, and resorption. In rats, there is some evidence for an association with restraint for implantation failure, but not for the morphological anomalies. Restraint in late gestation alters adult sexual behavior of male rat offspring, but consequences for their fertility are not known. Intrauterine growth retardation is not commonly associated with gestational restraint. In the few studies where they have been directly compared, different restraint procedures produced graded, qualitatively different, or no effects. Adrenocortical hormones have been implicated as mediating the effect of restraint on cleft palate, but not on supernumerary ribs, implantation failure, or sexual differentiation. Given the variety of restraint procedures and the varying species-dependent consequences, it is not possible to infer a generalizable pattern of developmental effects due to gestational stress from the restraint literature. As an alternative approach, contemporary methods in gene expression and developmental biology could profitably be applied to understanding different patterns of stress-mediated effects of toxicant exposures on intrauterine development.

Metallothionein is a component of exocrine pancreas secretion: implications for zinc homeostasis

Using transgenic mice that overexpress metallothionein-I (MT-I) and zinc-induced normal and transgenic animals, we have explored the localization of MT in the pancreas. Light-level immunocytochemistry demonstrated MT in acinar cells but not islet cells. Immunolabeling also revealed the presence of MT in pancreatic ducts, suggesting that it is released from acinar cells. Ultrastructural immunolocalization showed that MT was cytoplasmic, and no MT immunoreactivity was detected in lumens of the vesicular secretory pathway. Secreted pancreatic juice was collected from pilocarpine-stimulated mice and assayed for MT by a 109Cd-labeled hemoglobin-exchange assay and by radioimmunoassay. Both methods revealed high (> 1,000 ng/ml) levels of MT in the stimulated secretion. The level of MT in pancreatic juice from transgenic mice was only slightly (2-fold) increased despite dramatic overexpression of MT-I in the pancreas (> 20-fold). In contrast, zinc induction of MT significantly increased MT by 5- to 10-fold in the pancreatic juice, in normal and transgenic mice. These data indicate that MT is released from pancreatic acinar cells but not by the classical vesicular secretory pathway. In addition, MT levels in pancreatic juice are regulated by zinc, suggesting a physiological role of the pancreas in metal homeostasis.

Further observations on the etiology of pre-eclampsia: mobilization of toxic cadmium-metallothionein into the serum during pregnancy

Cadmium-metallothionein, mobilized from the liver, might be the toxic serum factor associated with pre-eclampsia. We base this on four documented concepts. First, during pregnancy, maternal physiology adjusts to assure the fetus of the proper amounts of nutrients necessary for growth. Our focus is on zinc and progesterone. Second, because zinc and cadmium are similar, they compete for binding sites. Our focus is on the storage protein metallothionein. Third, the manifestations of cadmium toxicity closely mimic the manifestations of toxemia (i.e. hypertension, proteinuria, edema). Our focus is on cadmium-induced endovasculitis. Fourth is the concept that metallothionein-bound cadmium can be mobilized from the liver into the serum during pregnancy as it follows the mobilization of metallothionein-bound zinc. Our focus is on the extreme toxicity of extracellular cadmium-metallothionein. We correlate these four concepts into a rational theory on the etiology of toxemia, and we suggest a method of proof.