Fish oils modulate blood pressure and vascular contractility in the rat and vascular contractility in the primate.

The effect of dietary fish oils on development of hypertension and vascular response in vitro were studied in rats and a primate. Dietary fish oils (MaxEPA and an n-3 ethyl ester concentrate of higher EPA and DHA content) were administered to spontaneously hypertensive (SHR), stroke-prone spontaneously hypertensive (SHR-SP) and a backcross of SHR and Wistar Kyoto (SHR/WKY) rats from 4-16 weeks of age. Blood pressure was monitored during the feeding period and vascular responses measured in the aorta and mesenteric vascular bed in vitro. Depending on the strain of rat used and the composition of the fish oil the attenuation in blood pressure was 10-26 mmHg. Fish oils attenuated the response mediated by sympathetic nerve stimulation or intralumenal norepinephrine in the perfused mesenteric vascular bed preparation from the SHR. This attenuation was more pronounced for fish oils enriched with eicosapentaenoic acid and docosahexaenoic acid and was more prominent in the SHR and SHR/WKY backcross than it was in the SHR-SP. Prostanoid synthesis or nitric oxide modulation of alpha-adrenoceptor responses were shown not to be involved in the attenuation of vascular responses produced by fish oil. The maximum contraction of aortic ring preparations in response to norepinephrine (NE) was significantly smaller in SHR than WKY rats fed olive oil and for SHR rats maintained on fish oils the contraction was close to WKY olive oil values. Evidence was obtained also for a modulation of vasoconstrictor responses by dietary fish oils in the perfused mesenteric bed of the marmoset monkey.

Interactions between 5-hydroxytryptamine, noradrenaline and the thromboxane-A2 mimetic U44069 in the marmoset isolated aorta.

1. The effects of 5-hydroxytryptamine (5-HT) in the absence and presence of noradrenaline (NA) or the thromboxane-A2 mimetic, U44069, were investigated in ring preparations of marmoset aorta. 2. 5-HT (0.001-10 mumol/L) produced little or no contractile response in preparations at basal tone. When the tone was elevated to 50% of maximum with NA the predominant response to 5-HT was relaxation. The 5-HT2 receptor antagonist LY53857 (0.1 mumol/L) unmasked a contractile response to low concentrations of 5-HT (0.01-1.0 mumol/L) and reduced relaxation to high concentrations of 5-HT (1.0-10 mumol/L) in vessels precontracted with NA. 3. In U44069-contracted vessels, 5-HT was contractile in the range 0.01-1 mumol/L and relaxant in concentrations of 6.0-10.0 mumol/L. Ketanserin (1.0 mumol/L) had no effect on the contraction or relaxation to 5-HT. 4. The relaxant response to 5-HT was not significantly diminished in endothelium-impaired arteries. 5. In conclusion, 5-HT exerts complex inhibitory and excitatory actions on the marmoset aorta. The inhibitory actions are not endothelium-dependent and the excitatory actions do not appear to involve the 5-HT2 receptor.

Dietary fish oil administration retards blood pressure development and influences vascular properties in the spontaneously hypertensive rat (SHR) but not in the stroke prone-spontaneously hypertensive rat (SHR-SP).

In the present study, we compared the blood pressure in the SHR-SP and in the spontaneously hypertensive rat (SHR) after dietary administration of fish oil from 4 to 17 weeks of age. The retarding influence of dietary fish oils on the development of hypertension was prominent in the SHR (26 mmHg) and not evident in the SHR-SP (8 mmHg). The enhanced development of blood pressure in both the SHR and the SHR-SP is characterised by an elevated maximum contraction in the mesenteric vascular bed to sympathetic nerve stimulation and to injected noradrenaline. In SHR, but not SHR-SP, this maximum contraction was significantly attenuated by dietary fish oil. Likewise, acetylcholine mediated relaxation of the isolated aorta was enhanced in preparations from the SHR but not the SHR-SP. These physiological changes were also associated with a change in the total n-3 polyunsaturated fatty acids (PUFAs) content in vascular tissue, which were inversely proportional to the prevailing blood pressure values seen in all three strains of rat receiving dietary fish oils. Platelet activated thromboxane production was equally depressed in WKY (Wistar Kyoto), SHR and SHR-SP rats. The results indicate that the blood pressure lowering effect of fish oil when administered during the period of development of hypertension is much greater in the SHR than it is in the SHR-SP. Furthermore the lowering of blood pressure by fish oil administration is related to a restoration of normal vascular contraction and normal vascular relaxation, but not related to a suppression of serum thromboxane production.

Influence of alpha 1- and alpha 2-adrenoceptor antagonist therapy on the development of hypertension in spontaneously hypertensive rats.

There is general agreement that the sympathetic nervous system is involved in the development of hypertension in spontaneously hypertensive rats (SHR). However, in a previous study we established that chronic administration of the selective alpha 1-adrenoceptor antagonist terazosin to SHR failed to prevent this phenomenon. In the present study, we extended that investigation further by examining the effects of another selective alpha 1-antagonist (doxazosin), an alpha 2-adrenoceptor antagonist (yohimbine), and a combination of these agents. Chronic administration of doxazosin and yohimbine produced receptor blockade, as determined by their effect on blood pressure (BP) responses to norepinephrine (NE) and phenylephrine. Chronic administration of either antagonist alone or the two in combination failed to prevent the development of hypertension in SHR, however. These findings suggest that although there may be a need for involvement of the sympathetic nervous system in the development of hypertension in SHR, its influence on this process is not mediated through activation of alpha-adrenoceptors.

Neurovascular function during pregnancy in the spontaneously hypertensive rat.

1. Blood pressure (BP) declines dramatically in the final week of gestation in the pregnant spontaneously hypertensive rat (SHR). This study investigated the hypothesis that alterations of vascular neuroeffector function in the pregnant SHR and normotensive Wistar-Kyoto (WKY) rat are responsible for this decline. 2. Pregnancy in SHR and WKY rats was associated with a significant drop in BP in the last week of gestation. 3. Responses of the perfused mesenteric vasculature to bolus doses of noradrenaline (NA) and potassium chloride (KCl) were decreased in preparations from SHR rats 4 days before delivery. This decreased responsiveness was absent in preparations from SHR rats 1 day before delivery. Responses of the perfused mesenteric vasculature to sympathetic nerve stimulation were not influenced by pregnancy in the SHR. 4. It is concluded that while there are dynamic changes occurring in neurovascular function just prior to delivery, it is unlikely that they are wholly responsible for the dramatic decline in blood pressure in the SHR rat.

Dietary fish oil administration retards the development of hypertension and influences vascular neuroeffector function in the stroke prone spontaneously hypertensive rat (SHRSP).

An influence of fish oils (rich in eicosapentaenoic acid, EPA) in modulating (a) the development of hypertension in the stroke prone spontaneously hypertensive rat (SHRSP) and (b) vascular neuroeffector mechanisms in the SHRSP was explored. Rats (SHRSP) were placed on a series of diets for a period of 13 weeks from 4 weeks of age. The fatty acid composition of the diets was derived from fish oil, olive oil, safflower oil or beef fat. After 13 weeks, rats fed diets containing fish oil (at a total dietary fat level of either 5% or 15%) had mean blood pressures approximately 20-25 mmHg lower than other SHRSP rats maintained on diets containing either olive oil, safflower oil or beef fat. The dietary schedules providing fish oil depressed the contractile responses mediated by sympathetic nerve stimulation in the mesenteric vascular bed preparation. The results suggest that the n-3 polyunsaturated fatty acids retard the development of hypertension in the SHRSP rat and modulate the contractile responses of blood vessels mediated by sympathetic nerves in the isolated perfused mesenteric vascular bed preparation.

The effect of thyroxine, 3, 5-dimethyl-3'isopropyl-L-thyronine and iodized oil on fetal brain development in the iodine-deficient sheep.

Studies have been carried out to investigate the role of maternal and fetal thyroid function in the effects of iodine deficiency on fetal brain development in sheep. Iodine deficiency was established with an especially prepared low-iodine diet of maize and pea pollard. The iodine-deficient sheep were mated and the end of the second trimester of pregnancy (100 days gestation) were divided into groups which received either a sc injection of T4 or 3,5-dimethyl-3-isopropyl-L-thyromine or an injection of iodized oil. AT 140 days gestation (10 days prior to parturition) comparison of the fetuses delivered by hysterotomy revealed that the retarded fetal brain development observed in iodine deficiency was greatly improved by T4 and by iodized oil. However, T4 and iodized oil failed to correct the reduction in the number and the increase in the length of synaptic appositions which were observed in the fetal cerebral cortex after iodine deficiency. In addition, the histological appearance of the fetal thyroid gland and the levels of plasma thyroid hormones were restored to normal. The administration of 3,5-dimethyl-3'-isopropyl-L-thyronine had no effect on the retarded fetal brain and body development of the iodine-deficient fetuses. The lack of response may be due to the ability of 3,5-dimethyl-3'-isopropyl-L-thyronine to cross the ovine placenta as no reduction in the abnormally elevated fetal plasma TSH observed in spite of a fall in maternal plasma TSH and apparent restoration of maternal thyroid function.(ABSTRACT TRUNCATED AT 250 WORDS)

A review of experimental studies of iodine deficiency during fetal development.

Iodine deficiency is now recognized as a major international public health problem. It is estimated that 800 million people may be at risk of the effects of iodine deficiency. In humans, the effects occur at all stages of development: the fetus, the neonate, the child and adult. The effects are now denoted by the term iodine deficiency disorders (IDD). They include miscarriages, stillbirths, congenital anomalies, as well as the more familiar goiter, cretinism, impaired brain function, and hypothyroidism in children and adults. In domestic animals, reproductive failure has been reported with the production of aborted, stillborn and weak calves. Experimental studies in animal models have been reviewed to provide evidence of the mechanisms involved, particularly in relation to brain development. The findings in three different species (rat, sheep, monkey) indicate that the effects are mediated by a combination of maternal and fetal hypothyroidism, the effect of maternal hypothyroidism being earlier than the onset of fetal thyroid secretion. The findings suggest that iodine deficiency has an early effect on neuroblast multiplication and, if so, this could be important in the pathogenesis of the neurological form of endemic cretinism. The assessment of the full effects of iodine deficiency on the brain requires further studies in the postnatal period to determine the duration of these effects.

Fetal brain development in response to iodine deficiency in a primate model (Callithrix jacchus jacchus).

The common cotton-eared marmoset (Callithrix jacchus jacchus) has been used for the first time as a primate model to study the effects of dietary iodine deficiency on fetal brain development. Paired male and female marmosets were fed a low-iodine diet of maize, peas, meat meal, Torula yeast, maize oil and added vitamins, minerals and amino acids for 6 months before mating. Offspring from first and second pregnancies were compared with offspring from control marmosets fed the same diet but supplemented with iodine. Severe iodine deficiency in the fetus at birth was evident by reduced plasma thyroxine levels, increased plasma thyroid stimulating hormone levels, increased thyroid weight and reduced thyroid iodine content. Thyroid histology revealed hyperplasia, hypertrophy and absence of colloid material in the follicles. Iodine deficiency caused a reduction in the weight of the fetal brain and in particular the cerebellum. Brain cell number was reduced in the cerebellum and brainstem but cell size was reduced in the cerebral hemispheres. Histology of the brain revealed morphological changes in the cerebellum and cerebral hemispheres. In the-cerebellum there was: an increase in the thickness of the external germinal layer indicative of impaired cell acquisition; a decrease in total area; a decrease in molecular layer area; and an increase in Purkinje cell (Pc) linear density due to a reduction in the length of the Pc line. The decrease in molecular layer area and increase in Pc linear density imply diminished ascending and lateral extension of Pc dendrites. Changes in the cerebral hemispheres consisted of an increase in the density of neuronal cell bodies in the granular band and a decrease in synaptic counts in the layer between the pia mater and supragranular band of the visual cortex. Offspring from second pregnancies compared to those from first pregnancies were more severely affected and associated with lower plasma levels of maternal and fetal thyroxine. These findings indicate the importance of maternal and fetal thyroid function in relation to fetal brain development in the primate.

The effect of maternal thyroidectomy prior to conception on foetal brain development in sheep.

Merino ewes were surgically thyroidectomized, and mated 6 weeks later when their plasma thyroxine (T4) levels were negligible. Their foetuses were delivered by hysterotomy at 52, 71, 84, 98, 125, 140 days gestation or at term (150 days). Despite the very low levels of T4 in maternal plasma, the concentrations of T4 in foetal plasma were not significantly different after 71 days gestation from those of foetuses of sham-operated (control) ewes. Foetal brain and body weights, however, were reduced from 71 days compared to those of foetuses of sham-operated ewes. The foetal brain weights but not the body weights were restored to normal from 125 days to term. In addition to the weights, cell number (DNA) and cell size (protein:DNA ratio) appeared to be normal in the neonatal brain at parturition and this was confirmed by histological examination of the brains. Thus lack of maternal thyroid hormones in early pregnancy may cause a reduction in brain and body growth in the foetus which, in the case of the brain, appears to be restored to normal after the onset of foetal thyroid function.

Low-iodine diet for the production of severe I deficiency in marmosets (Callithrix jacchus jacchus).

A low-iodine diet consisting of maize, peas (Pisum sativum), torula yeast, meat meal, maize oil and added vitamins, minerals and amino acids was given to eight pairs of adult, common cotton-eared marmosets (Callithrix jacchus jacchus). Eight control pairs were given the same diet to which potassium iodate was added. Both groups also received low-I apple and deionized water. The diet provided adequate nutrition, as confirmed by the maintenance of body-weight and good health. In the I-deficient marmosets the concentration of plasma thyroxine was decreased from 140.1 nmol/l to 22.4 nmol/l and thyroid-stimulating hormone increased significantly from 1.8 ng/ml to 9.0 ng/ml compared with control marmosets, thereby indicating severe I deficiency. Compared with newborn offspring from control marmosets, the thyroid glands from the I-deficient offspring showed an increase in weight, a decrease in I content and, on histological examination, hyperplasia, hypertrophy and a total absence of colloid material in the follicles.

Restoration of brain growth in fetal sheep after iodized oil administration to pregnant iodine-deficient ewes.

Iodized oil was administered as a single intramuscular injection to pregnant iodine-deficient ewes at 100 days gestation and the subsequent growth of their fetuses compared with that of fetuses of severely iodine-deficient ewes and of iodine-replete ewes, all of which were fed the same low-iodine diet. The administered iodine produced a remarkable improvement in thyroid function and physical appearance of the fetuses, accompanied by an increase in brain growth and to a lesser extent in body growth, which at 140 days was only slightly (but significantly) less than that of the controls. There was restoration of the number of cells (DNA) and myelination (cholesterol/DNA) in the cerebellum and cerebral hemispheres which suggests a catch-up of neuroblast development during pregnancy. Histological examination, however, revealed that counts of synapses (density) in the cerebral cortex after iodized oil were still less than those of the control fetal brains. The relevance of these findings to the effects of iodine deficiency on human brain development is discussed.

The effect of maternal and fetal thyroidectomy on fetal brain development in the sheep.

The combination of maternal and fetal thyroidectomy was found to have a significant influence on brain development in the fetal sheep at 140 days. There was reduced body weight (36%), brain weight (23%), DNA (26%) and protein (34%) content in five fetuses of ewes, subjected to thyroidectomy six weeks before mating and fetal thyroidectomy at 98 days gestation, compared with six sham operated controls. Cholesterol content was also reduced (36%) and water content increased (2.4%). The cerebellum was most severely affected and showed histologically an increased cell density associated with a significant reduction in the ratio of the molecular to granular cell layer area. The cell density was also significantly increased in the CA1 region of the hippocampus, but not in the CA4 region. It was also increased in the parietal layer of the cerebral cortex but not in the motor region. There was a significant reduction in the weight of heart (28.6%) and lungs (33.4%), while the kidneys and pituitary were enlarged (20.5% and 48.5% respectively) as a result of double thyroidectomy. The combined thyroidectomy was similar to iodine deficiency in its effect on fetal brain development, indicating that it is probable that iodine deficiency has its effects in the sheep by a combination of maternal and fetal hypothyroidism.

Retarded fetal brain development resulting from severe dietary iodine deficiency in sheep.

Sheep have been used to study the effect of dietary iodine deficiency on the development of the fetal brain. Severe iodine deficiency caused reduction in fetal brain and body weights and in brain DNA and protein from 70 days gestation to parturition. The lowered brain weight and brain DNA at 70 days gestation indicates a reduced number of cells, probably due to slower neuroblast multiplication which normally occurs from 40-80 days in the sheep, and the reduction in DNA and protein after 80 days implies that the development of neuroglia could be slowed also in iodine deficiency. Morphological changes were observed in both the cerebral hemispheres and the cerebellum. In the cerebral hemispheres of the iodine-deficient fetuses an increased density of neurons was apparent histologically in the motor cortex and visual cortex and in the CA1 and CA4 areas of the hippocampus in comparison with controls. In the cerebellum there was delayed migration of cells from the external granular layer to the internal granular layer and increased density of Purkinje cells in the iodine-deficient fetal brains. In addition, the molecular area was increased and the medullary area reduced in comparison with controls. These change are indicative of delayed brain maturation. Evidence of fetal hypothyroidism was provided by low fetal thyroid iodine and plasma T4 values, thyroid hyperplasia from 70 days gestation, significant reduction in body weight at the same time as the brain retardation, and absence of wool growth and delayed skeletal maturation near parturition. It is apparent from the biochemical and histological changes observed during iodine deficiency that iodine is an essential element for normal fetal brain and physical development in the sheep.

Iodine deficiency and brain development in the rat.

An assessment was made of the influence of low-iodine diet on somatic and brain development at birth (day 0) and 21 days postnatally in the rat. The rat mothers were proven to be iodine-deficient by assay of plasma thyroxine and thyroid stimulating hormone prior to mating, an at 21 days postnatally, when maternal thyroids were removed, weighed and stored for subsequent iodine analysis, along with those of the offspring. There were no significant differences in body weight or brain weight of the offspring at birth, or in the content of DNA or protein. However, at 21 days there was a significant reduction in body weight (21.7%) and whole brain weight (7.9%, P less than 0.2) which was associated with a significant fall n cholesterol content (12.4%, P less than 0.05) and protein level (9.6 %, P less than 0.01), while DNA was not significantly affected (6%). The greatest reduction in weight was seen in the cerebellum. The thyroids in these rats were double normal size, showed follicular cell hypertrophy and absence of colloid histologically, and contained 8% of the iodine content of controls. It is concluded that iodine deficiency retards both somatic and brain development, the change in the latter case being expressed as a reduction in cell size in the cerebral hemispheres and cerebellum, along with reduced myelination throughout the brain.

Experimental production of growth retardation in the sheep fetus after exposure to alcohol.

The effect of excessive alcohol consumption during pregnancy on fetal development has been studied in sheep. Fetuses of ewes which had consumed 10% ethanol in water before, and during, pregnancy were delivered by hysterotomy 10 days before parturition and found to be shorter (P < 0.01), lighter (P < 0.01), and to have significantly lighter brains (P < 0.05) than normal fetuses of comparable gestational age. Heart, liver, spleen, kidneys and adrenal glands all weighed less than those of fetuses from ewes which drank water instead of alcohol. The findings provide experimental evidence for growth retardation after exposure of the sheep fetus to alcohol, and are consistent with clinical reports on the human fetal alcohol syndrome.