Cutaneous sudomotor function in healthy individuals

Doyle, A (2025) Cutaneous sudomotor function in healthy individuals. Other thesis, LJMU.

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Abstract

Human perspiration or sweating is a vital physiological process that plays a crucial role in thermoregulation and maintaining homeostasis. Sweating is a critical response for losing heat in order to ensure appropriate maintenance of core body temperature. Sweating can also occur as part of the response to non-thermoregulatory events such as psychological stress. Sweating occurs via eccrine and apocrine sweat glands, which respond in different magnitudes to various stimuli, including heat, physical activity and mental stress. Eccrine glands, distributed widely across the skin, are primarily responsible for cooling the body through the secretion of a dilute saline solution, which evaporates and dissipates heat. In contrast, apocrine glands, located in specific areas such as the armpits and groin, mostly become active during mental stress and are associated with the production of a thicker, odoriferous secretion. The activation of these glands is regulated by the autonomic nervous system, with acetylcholine serving as the primary neurotransmitter, while adrenergic stimulation can also trigger sweating, especially in response to mental stimuli.
There are many situations and or conditions where sweating can be impaired or accentuated which can significantly affect quality of life. For example, hot flushes are the most common symptom of the female menopause; a milestone of every female’s life typically between the ages of 45-55 years. Hot flushes are a sudden, intense sensation of heat causing skin reddening, flushing and profuse sweating. The mechanisms of a hot flush, especially as it pertains to the skin and the sweating that occurs, are unclear, however. Furthermore, sweating from apocrine glands can cause malodour and damage clothes. Personal hygiene products, such as antiperspirants, have become essential to combat body malodour and excessive axillae perspiration. Evaluating and analysing the effectiveness of these products is crucial for companies to ensure product quality. The knowledge of axillary sweating responses to various everyday activities such as exercise, heat exposure and mental stress is scarce, however. Understanding the mechanisms and functions of sweating in these situations is essential for further understanding the pathophysiology and the development of strategies for hot flushes and apocrine sweating. The overall aim of this thesis is to therefore examine the control of cutaneous sudomotor responses in healthy individuals in response to common physiological conditions that affect this process. The specific objectives are 1). To develop a sound protocol, informed by information collected from the literature, to assess both function and structure of skin blood vessels and sweat glands in premenopausal and postmenopausal women both with and without hot flushes and 2). To examine the local axilla sweating responses to different forms of stress that trigger sweating in the axilla region in young healthy females. In order to achieve aim #1 a protocol was designed involving 3 distinct groups: postmenopausal women who experience hot flushes, postmenopausal women who do not experience hot flushes, and a young, healthy premenopausal group. The structure and function of skin blood vessels and sweat glands of these 3 groups will be assessed using the microdialysis and skin punch biopsy methods. Visit 1 involves the evaluation of post-ganglionic skin blood vessel and sweat gland responsiveness using transdermal/cutaneous microdialysis for the intradermal administration of pharmacological agents to assess skin blood flow and sweating Dose-response curves for skin blood flow and sweating will be created, and EC50 values will be estimated (increasing doses of acetylcholine, sodium nitroprusside, or CGRP). For Visit 2, a skin punch biopsy will be performed from the same site to assess the structure of skin blood vessels and sweat glands. Samples will be sectioned, stained for blood vessels and sweat glands, will be analysed using confocal microscopy to evaluate the number and size of blood vessels and sweat gland secretory coils. .By comparing the three groups, the study hopes to identify any differences in cutaneous structure and function that may contribute to our understanding of how menopause, and the presence or absence of hot flushes, affects skin physiology.

In order to achieve aim #2 the sweating responses of female participants across three conditions; exercise, passive heating, and mental stress were investigated. Visit 1 involved a 2-hour exercise protocol at room temperature (~18°C, ~40% rh), Visit 2 consisted of passive heat exposure in a heated room (~40°C, ~30% rh), and Visit 3 involved a battery of mental stress tests with cognitive challenges. 30 females took part in the three trials (27±7 years, 63±8 kg, 161±7 cm). Two participants were postmenopausal, and two were using oral contraceptives. Local axillary sweating responses were measured using two methods. The SweatSENSE method involved placing small paper sensors on the left and right axilla for 5 seconds, with the colour change analyzed to index sweating activity. Continuous sweating was also measured from the left axilla using capacitance hygrometry. Significant main effects of time and condition (P < 0.01) were observed, along with significant time × condition interactions (P < 0.01), indicating distinct sweating profiles across conditions. The results indicated that sweating was highest during the exercise condition, as demonstrated by both capacitance hygrometry data and Sweatsense measurements followed by passive heating then emotional stress. Exercise elicited the most pronounced and intermittent sweating response, while passive heating and mental stress produced more gradual and consistent increases. A significant main effect of condition was observed (P < 0.001), indicating overall differences in core temperature across trials. Core temperature was highest during the exercise condition (37.3 °C), followed by emotional stress (37.0 °C) and passive heating (36.8 °C). While core temperature increased over time (P = 0.006), there was no significant time × condition interaction (P = 0.124). Skin temperature was highest during passive heating (34.5°C followed by emotional stress (32.1°C ) then the exercise trial (31.6°C). Skin temperature remained elevated and stable during passive heating. In contrast, emotional stress induced an initial rise followed by a gradual decline across sites, while exercise led to variable responses, with increases at the thigh and calf, but decreases or plateaus at the forearm and axilla." By comparing the sweating responses across these conditions, the study provided valuable data that could contribute to the development of more effective antiperspirants and enhance the understanding of the physiological mechanisms underlying sweating.

In summary, this thesis investigated the physiological mechanisms of sweating, focusing on the structural and functional properties of skin blood vessels and sweat glands in premenopausal and postmenopausal women, with and without hot flushes, and examines local axillary sweating responses across different stressors. Using advanced methods, including microdialysis, skin punch biopsies, the SweatSENSE technique, and capacitance hygrometry, the findings deepened our understanding of sweating mechanisms and help to inform the development of more effective antiperspirants, while also shedding light on the relationship between menopause and sweating.

Item Type:	Thesis (Other)
Uncontrolled Keywords:	Thermoregulation; Menopause; Cutaneous sudomotor function; Female; Physiology
Subjects:	R Medicine > RC Internal medicine > RC1200 Sports Medicine
Divisions:	Sport and Exercise Sciences
Date of acceptance:	15 May 2025
Date Deposited:	24 Jun 2025 09:23
Last Modified:	24 Jun 2025 09:24
DOI or ID number:	10.24377/LJMU.t.00026410
Supervisors:	Low, D, Jones, H and Roberts, K
URI:	https://researchonline.ljmu.ac.uk/id/eprint/26410

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