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Biomedical subjects

A C Shipstone

Publications and source records attributed to A C Shipstone.

At least 19 recordsLinked to original sources
PubMed1988

Effects of sodium deoxycholate on the mechanical and electrical activities and ultrastructure of guinea pig atria.

The mechanism of cardio-inhibitory effects of sodium deoxycholate (DOC) was investigated by studying its effects on the contractility, action potentials (APs) and ultrastructure of guinea pig atrial preparations. DOC (10(-7)-10(-4) M) caused reversible negative ino- (NIE) and chrono-tropy in spontaneously beating (SBA) and NIE in electrically driven left (EDA) atria. At higher doses (greater than or equal to 1.10(-3) M) DOC caused irreversible inhibition of contractions. Atropine (10(-7)-10(-4) M) failed to inhibit both the reversible and irreversible effects of DOC. The NIE due to lower doses of DOC (less than or equal to 1.10(-4) M) was inhibited by higher [Ca2+]0, isoprenaline (10(-6)-10(-4) M), and noradrenaline (10(-6)-10(-5) M), which did not alter the dose of DOC required for the irreversible and complete NIE. In lower doses (10(-7)-10(-4) M) DOC caused a reversible inhibition of the AP durations at -20 and -40 mV (APD20 and APD40, respectively), but increased the AP duration at 90% repolarisation (APD90). At higher doses (greater than 5.10(-4) M) it caused an irreversible membrane depolarization, reduction in APD20 and APD40, and complete cessation of electrical activity. The ultrastructural changes in atria treated with 1.10(-4) M DOC were characterized by poorly delineated glycocalyx and at greater than 1.10(-3) M by disruption of sarcolemma and sarcoplasmic reticulum and swelling disruption of mitochondria. Taken together these observations show that DOC caused reversible and irreversible inhibition of atrial contractions at low (10(-7)-10(-4) M) and high (greater than 5.10(-4) M) concentrations, respectively, by different mechanisms. The former effect is due to inhibition of Ca2+ channel activity and the latter due to its detergent property causing removal of subcellular components.

Action Potentials↗
PubMed1983

Ultrastructural changes in the neural lobe of the rat pituitary following nicotine pretreatment.

The effect of nicotine on the ultrastructural changes and hormone contents of the neural lobe of the pituitary were studied in the rat. Nicotine caused a significant release of both vasopressin and oxytocin from the neural lobe. The examination of the neural lobe with electron microscope reveals the nerve terminals depleted of neurosecretory granules. These results suggest that a definite correlation exists between hormone contents and ultrastructural morphology.

Animals↗
PubMed1982

Scanning and transmission electron microscopy of the ependyma of the fourth ventricle in the monkey brain.

The ependymal structure of the fourth ventricle floor of adult rhesus monkeys was investigated using both scanning and transmission electron microscopy. Each half of the floor exhibited dense ciliation which decreased towards the median sulcus. The area postrema and the facial colliculus lacked cilia and were covered with non-ciliated ependymal cells. Along the entire length of the median sulcus supraependymal globular protrusions were seen. Over the rostral and middle thirds of the sulcus these protrusions exhibited interwoven ridges. At the former situation they were closely approximated but at the latter they were on the surface of non-ciliated nodules which were lying amongst sparsely ciliated cells. In the caudal third these protrusions presented smoother surfaces without any structural details over them. Transmission electron microscopy through the upper two thirds of the median sulcus revealed these surface protrusions to be non-ciliated cells having long and profuse network of interwoven microvilli over their luminal surface. These cell bodies exhibited well-defined supranuclear Golgi complexes, vesiculated rough and smooth surfaced endoplasmic reticulum, free ribosomes and polyribosomes, few electron dense granules, network of microtubules and light and dense multivesiculated bodies. These features suggested a secretory and/or absorptive role, rather that autophagy to these surface specialization.

Animals↗
PubMed1979

The effect of estrogen on the tubal epithelium of immature ovariectomized rhesus monkey (Macaca mulatta).

The effect of 3 doses of estradiol dipropionate (EDP) on tubal epithelium of immature ovariectomized rhesus monkey (Macaca mulatta) was studied under both light and electron microscopy. EDP at a dose of 5 microgram/kg/day for 6 consecutive days changed differentiation of the epithelial cells into clear and dark cell-types; ciliogenesis, formation of some ciliary buds and even a few cilia were also induced in some clear cells throughout the tubal epithelium. Development of ciliated cells with fully formed ciliary apparatus was accelerated at 10 microgram/kg dosage. The secretory granules (SG) appeared at this dose in some nonciliated cells of the infundibular and ampullary but not the isthmic segments of the tube; some of the infundibular secretory cells, so formed, exhibited even a tendency to secrete. Nearly complete maturation of the tubal epithelium occurred at 20 microgram/kg dose; further signs of secretory activity appeared in all tubal segments. The results indicated that--(i) Nearly complete transformation of tubal epithelium of the immature animal into one of the adult type could be achieved by EDP at a dose not less than 20 microgram/kg under the present conditions. (ii) The response of undifferentiated cells to EDP differed depending upon the location of the epithelial cell within the tube and nature of the cell-type to be formed. (iii) The mode of tubal secretion in this infra-human species was probably apocrine.

Animals↗
PubMed1979

The effect of estrogen withdrawal upon the tubal epithelium of immature ovariectomized rhesus monkey (Macaca mulatta) pretreated with estradiol dipropionate.

Immature ovariectomized rhesus monkey (Macaca mulatta) were injected intramuscuarly with estradiol dipropionate (EDP) at a dose of 20 micrograms/kg/day for 6 consecutive days and were sacrificed at days 1, 3, 8, 13 and 25 following withdrawal of the hormone. The overall height of the epithelia of the infundibulum (Inf), Ampulla (A) and the isthmus (I) and the status of the ciliated and nonciliated cells therein were observed under both the light and electron microscope and those observed at days 3-25 were assessed against those found at day 1 (control values). The EDP effect on the above aspects did not change significantly at days 3 and 8 as compared to day 1. There was rather an increase of such hormone impact on day 8: this is indicated by the observations that the nonciliated cells possessed a greater number of secretory granules (SG) and/or exhibited signs of higher secretory activity. Possible neosynthesis of SG was discerned on days 3 and 8. Retrogressive changes in the epithelia and in the constituent cell types were evident on day 13; those advanced further on day 25 but to different degrees in different segments. The changes were highest in Inf following by those in A and I in order: Inf greater than A greater than I. All these changes were described and commented upon. It is concluded that the estrogen impact lasts for some time after its withdrawal and that the nature of subsequent regression of any epithelium and of the celltype therein is determined by their position within the tube.

Animals↗
PubMed1977

Electron microscope study of thallium-induced alterations in the oligodendrocytes of the rat area postrema.

Thallotoxicosis following accidental ingestion of thallium in rodenticides and in cases of homicidal and suicidal ingestion are well documented in the literature. The mechanism of action of thallium, in particular the pathogenesis of its neurotoxic manifestations, is not entirely clear. This is the first electron microscopic investigation dealing with the effect of thallium on the oligodendrocytes of the area postrema. The area postrema is devoid of a blood-brain barrier, indicating that the hemoneural transport of thallous ions may be quite substantial in this region. Rats weighing 155-175 g were given intraperitoneal injections of 5 mg/kg thallous acetate for 7 days (35 mg/kg total dose). Following perfusion-fixation, ultrathin sections of area postrema were examined with an electron microscope. The oligodendrocytes exhibited pleomorphic vacuolated dense bodies in their perikaryon. The findings were also suggestive of the fact that either the multiplication of oligodendrocytes or their aggregation to form "giant cell" was operative.

Animals↗
PubMed1977

Differential response of the ampullary and isthmic cells to ovariectomy and estrogen treatment: an ultrastructural study.

Ultrastructural response of the ciliated and secretory cells from the ampullary and isthmic parts of the oviduct was studied in ovariectomized and ovariectomized plus estradiol dipropionate (EDP) treated rabbits. Ovariectomy did not significantly affect the cilia in the ampullary epithelium; degenerative signs, however, appeared overtly in the isthmic cilia. EDP at either 1 microng/kg or 5 microng/kg doses raised the number of cilia/cell in either tubal segments. For comparable change isthmic cilia seemed to require a higher dosage of the estrogen. Ovariectomy led to the depletion of the secretory granules (SGs) from the secretory cells of either tubal segments. EDP at both the doses induced formation of the SGs; this is more remarkable in the isthmic cells. Merocrine type of secretions were observed from the secretory cells of either segments but only at the high dose of estrogen. The findings are discussed in the backdrop of current knowledge.

Animals↗