Date of Award

5-2002

Document Type

Thesis

Degree Name

Master of Science (MS)

Department

Environmental Science

First Advisor

Dr. Mustafa A. Ayoub

Second Advisor

Taher EI- Sharkawy

Third Advisor

Riad Bayoumi

Abstract

Birth defects are anatomical abnormalities present at birth. The causes of birth defects are genetic, environmental and multifactorial inheritance factors. The main objective of the thesis is to determine the effects of maternal heat stress during rat pregnancy on fetal axial skeletal development and to explore some of the possible maternal and placental responses to heat stress.

Experiment one: A group of 40 Wistar pregnant rats were randomly assigned to two treatment groups, a control group (non-stressed, n = 10) heat at 21°C and a heat-stressed group kept at 41 °C (n = 30) for one hour on day 9 of gestation. The objective of this experiment is to determine the effect of heat stress on some maternal physiological parameters. Following an hour of heat stress or sham treatment, blood samples were collected from orbital vein, allowed to clot, and centrifuged at 3000 r.p.m for 10 minutes to obtain serum. Serum samples were used for determination of glucose, calcium, osteocalcin, thyroxin (T4) and triiodothyronine (T3).

Results showed that heat stress caused significant Increases In serum glucose and oseocalcin levels. In addition, serum calcium, T3, and T4 levels were significantly lower in treated animals than those in control group.

Experiment two: A total of 34 Wistar pregnant rats were randomly assigned to three treatment groups, a control group (non-stressed, n = 10) kept at 21°C, a heat-stressed group I kept at 41°C (n = 14), and a heat-stressed group II kept at 42°C (n = 10) for one hour on day 9 of gestation. The objective of this experiment is to investigate the effect of heat stress on embryonic bone development and to demonstrate the extreme changes and severity of skeletal malformations due to temperature.

Results showed that heat stress caused reduction in the implantation, number of live embryos and fetal and placental weights in comparison to control animals. These effects were significantly pronounced in the 42°C treatment group. Morphological malformations were found in fetuses due to heat treatment. Malformations in the upper and lower jaws and increased incidence of mandibular and maxillary hypoplasia were observed in heat-treated group as compared to the controls. But in comparison between 41°C and 42°C, the 41°C group showed a higher incidence of maxillary-mandibular hypoplasia and tongue protrusion. In addition, both experimental groups showed a high incidence of excencephaly, exopthamia with cataract, facial clefts, and short tails than the controls.

More skeletal malformations were recorded in experimental animals than in controls. The control fetuses had well ossified bones of the skull that included the mandible, premaxilla, maxilla, zygomatic, nasal, frontal, parietal, interparietal, supraoccipital, exoccipital, temporal, tympanic ring, hyoid, ethmoid, presphenoid, basisphenoid and basioccipital bones than in the experimental animals. The comparison between 41°C and 42°C groups showed different responses in terms of skeletal defects.

Also results showed that control vertebral column appeared to have higher ossified vertebra than experimental groups. In the experimental fetuses, the vertebral arches and bodies showed decrease in number and poor ossification. The higher the temperature, the higher was the reduction in number of lumbar, sacral and coccygeal arches and bodies in experimental groups.

In the control group, ribs, and sternebare appeared normally ossified without any reduction in number. No instance of fused or hypoplastic ribs was found in control fetuses. There was lower incidence of hypoplastic ilium, ishchium and pubis in control fetuses than in experimental rats. In addition, higher development in forelimb skeletons was observed in the control animals than in the treated ones.

Placentas of the control groups showed lower weight compared with the experimental groups. The deciduas of experimental group was thicker than that of control group. There were large areas of hyalinization and lymphatic infiltration. Multinucleated giant cells were more abundant than those with single nucleus and basophils were extremely numerous. The glycogen cell clusters were reduced or absent over a large proportion of the spongy zone. Electron microscopic examination of the placentas showed a series of degenerative changes in experimental groups higher than those in control group placentas.

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