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Biomedical subjects

M Fitzgerald

Publications and source records attributed to M Fitzgerald.

At least 109 records · Page 6Linked to original sources
PubMed1980

Haemodynamic effects of increasing extracellular potassium concentration in ACTH-induced hypertension in sheep.

1. ACTH administration (20 microgram day-1 kg-1) to sheep produces hypertension associated with a raised cardiac output and hypokalaemia. 2. The aim of the present experiments was to detail the haemodynamic changes associated with restoration of the extracellular potassium concentration in sheep with ACTH-induced hypertension. 3. After 7 days of ACTH treatment potassium chloride (10 mmol/h) was infused for 3 days to restore plasma [K+] to the pre-ACTH value. 4. ACTH reduced plasma [K+] from 4.4 +/- 0.1 to 3.2 +/- 0.2 mmol/l but 3 days of potassium chloride infusion returned plasma [K+] to 4.3 +/- 0.2 mmol/l. 5. ACTH increased mean arterial pressure from 67 +/- 2 to 88 +/- 1 mmHg in the first 7 days and it remained elevated during potassium chloride infusion (91 +/- 5 mmHg on day 10). 6. Cardiac output rose with 7 days ACTH treatment from 4.9 +/- 0.2 to 6.0 +/- 0.6 l/min but fell progressively with potassium chloride infusion to 4.9 +/- 0.3 l/min on day 10. 7. These studies suggest that potassium status or extracellular [K+] may play a role in determining the haemodynamic profile associated with steroid-induced hypertension.

Adrenocorticotropic Hormone↗
PubMed1979

The spread of sensitization of polymodal nociceptors in the rabbit from nearby injury and by antidromic nerve stimulation.

1. Ninety-three polymodal nociceptor units with unmyelinated axons were isolated from rabbit sural nerves. Twenty-three were used for control data. These showed normal sensitization on repeated heating of their receptive fields, measured here as a drop in mean heat threshold. 2. Small injuries were made 5 (n = 15) or 10 (n = 12) mm outside the receptive fields of some polymodal nociceptors. This resulted in the development of spontaneous firing and lowered thresholds to heating of the receptive field. 3. Local anaesthetic previously injected into the site of injury blocked this spread of heat sensitization. Previous injection of saline had no effect. 4. Antidromic stimulation of the sural nerve, proximal to the recording site, also resulted in heat sensitization of polymodal nociceptors (n = 10). 5. Possible mechanisms for the spread of sensitization of polymodal nociceptors from nearby injury are discussed. Analogies are drawn between these results and those of Lewis (1935--36) on the spread of cutaneous ;yperalgesia around a skin injury in man.

Action Potentials↗
PubMed1979

Cellular mechanics of dentinal bridge repair using 3H-thymidine.

Cellular reorganization in the pulp following mechanical pulp exposure involves three steps: First, lysis and macrophage resolution of the clot form; second, there is an invasion of the clot area by fibroblasts and endothelial cells, i.e., formation of granulation tissue; third, an organization and differentiation of these cells into functional odontoblasts occurs as early as 9 days after exposure. Autoradiographic results showed an increased DNA synthesis in the fibroblast and endothelial cell populations which coincided with a histologically-observed increase in those populations. A relative increase in fibroblastic activity, as compared to endothelial cell activity, suggested that fibroblasts may be the cells that replace odontoblasts.

Animals↗
PubMed1977

The sensitization of high threshold mechanoreceptors with myelinated axons by repeated heating.

1. Seventy high threshold mechanoreceptor units (HTMs) with myelinated axons were isolated from the sural nerves of cats and rabbits. Thirteen cat and forty-two rabbit HTMs were testec by controlled, repeated heating of the skin of the foot or lower leg to noxious levels. 2. Many of the units (77% in the cat and 40% in the rabbit) fired to heating. Only six (11%) of these fired to the first brief heating to 50-55 degrees C. The rest required 2-6 heat trials before responding. 3. Heat responding units always became more sensitive with repeated heat stimulation but their mechanical sensitivity showed no comparable changes when heat sensitization occurred. 4. If these results are applicable to man, they suggest that HTMs play little role in generating the first pain that follows skin heating but that they may be involved in the increased sensitivity to heat pain (hyperalgesia) shown by skin previously injured by heating.

Action Potentials↗
PubMedDate not supplied

Spontaneous and evoked activity of fetal primary afferents in vivo.

The first movements of the fetus are apparently random and spontaneous. Their onset coincides with the growth of dorsal root afferents into the spinal cord and it is possible that they are not simply a result of spontaneous motoneuron activity but are reflex responses to sensory stimulation. It is not clear what stimuli could normally evoke such reflexes because nothing is known of the properties of primary afferent neurons in the fetus. I have investigated this by making recordings from single dorsal root ganglion cells in fetal rats in vivo. The afferents have small, defined receptive fields and respond to mechanical stimulation of skin or muscle at intensities that might occur in utero. Many of them are also chemosensitive. Unlike postnatal afferents they display background activity which peaks at the same age as fetal movements. Repeated stimulation causes long-lasting increases of both background and evoked activity. Such sensory input is likely to have a considerable influence on fetal movements and on the development of spinal cord connections.

Animals↗