Publisher Summary The chapter collates available data on the physicochemical characteristics of the plasma lipoproteins and their apolipoproteins in mammals in such a way as to provide both a rapid access to the main features of the lipid transport system in each species and to facilitate a ready comparison between them. When studies of lipoprotein and apolipoprotein profiles are initiated in animals in which little prior information is available, techniques of isopycnic density gradient ultracentrifugation may profitably be applied. In the vast majority of mammals, high-density lipoproteins are the predominant class, and may account for up to 80% of the total substances. In man, the bulk of the circulating cholesterol is transported in esterified form as LDL; however, this is not the case in the majority of mammals in which HDL is often the primary cholesterol carrier. The microviscosities of the lipid domains of rabbit, bovine, and porcine lipoproteins differed little from those of the corresponding human particles, apart from the elevated microviscosity of bovine HDL, indicative of significant lipid–protein interaction. However, the molecular biological studies are now providing an insight not only into the amino acid sequences of mammalian apoproteins, but also into the proteolytic processing of the nascent polypeptides and into the structure and modulation of their genes.

Comparative analysis of mammalian plasma lipoproteins.

Hair's importance in human communication means that abnormalities like excess hair in hirsutism or hair loss in alopecia cause psychological distress. Androgens are the main regulator of human hair follicles, changing small vellus follicles producing tiny, virtually invisible hairs into larger intermediate and terminal follicles making bigger, pigmented hairs. The response to androgens varies with the body site as it is specific to the hair follicle itself. Normally around puberty, androgens stimulate axillary and pubic hair in both sexes, plus the beard, etc. in men, while later they may also inhibit scalp hair growth causing androgenetic alopecia. Androgens act within the follicle to alter the mesenchyme–epithelial cell interactions, changing the length of time the hair is growing, the dermal papilla size and dermal papilla cell, keratinocyte and melanocyte activity. Greater understanding of the mechanisms of androgen action in follicles should improve therapies for poorly controlled hair disorders like hirsutism and alopecia.

Androgens and hair growth

The rodent hindlimb unloading (HU) model was developed in the 1980s to make it possible to study mechanisms, responses, and treatments for the adverse consequences of spaceflight. Decades before development of the HU model, weightlessness was predicted to yield deficits in the principal tissues responsible for structure and movement on Earth, primarily muscle and bone. Indeed, results from early spaceflight and HU experiments confirmed the expected sensitivity of the musculoskeletal system to gravity loading. Results from human and animal spaceflight and HU experiments show that nearly all organ systems and tissues studied display some measurable changes, albeit sometimes minor and of uncertain relevance to astronaut health. The focus of this review is to examine key HU results for various organ systems including those related to stress; the immune, cardiovascular, and nervous systems; vision changes; and wound healing. Analysis of the validity of the HU model is important given its potential value for both hypothesis testing and countermeasure development.

Hindlimb unloading: rodent analog for microgravity.

Visual impairment intracranial pressure (VIIP) syndrome is considered an unexplained major risk for future long-duration spaceflight. NASA recently redefined this syndrome as Spaceflight-Associated Neuro-ocular Syndrome (SANS). Evidence thus reviewed supports that chronic, mildly elevated intracranial pressure (ICP) in space (as opposed to more variable ICP with posture and activity on Earth) is largely accounted for by loss of hydrostatic pressures and altered hemodynamics in the intracranial circulation and the cerebrospinal fluid system. In space, an elevated pressure gradient across the lamina cribrosa, caused by a chronic but mildly elevated ICP, likely elicits adaptations of multiple structures and fluid systems in the eye which manifest themselves as the VIIP syndrome. A chronic mismatch between ICP and intraocular pressure (IOP) in space may acclimate the optic nerve head, lamina cribrosa, and optic nerve subarachnoid space to a condition that is maladaptive to Earth, all contributing to the pathogenesis of space VIIP syndrome. Relevant findings help to evaluate whether artificial gravity is an appropriate countermeasure to prevent this seemingly adverse effect of long-duration spaceflight.

Spaceflight-Induced Intracranial Hypertension and Visual Impairment: Pathophysiology and Countermeasures.

Disorders of Hair

Thyroid and gonadal regulation of hair growth during the seasonal molt in the male European badger, Meles meles L

Changes in apical organization of choroidal cells in rats adapted to spaceflight or head-down tilt.

To determine when choroidal structures were restored after readaptation to Earth gravity or orthostatic position, fine structure and protein distribution were studied in rat choroid plexus dissected either 6 h [Space Life Sciences-2 (SLS-2) experiments] or 2 days [National Institutes of Health-Rodent 1 (NIH-R1) experiments] after a spaceflight, or 6 h after head-down tilt (HDT) experiments. Apical alterations were noted in choroidal cells from SLS-2 and HDT animals, confirming that weightlessness impaired choroidal structures and functions. However, the presence of small apical microvilli and kinocilia and the absence of vesicle accumulations showed that the apical organization began to be restored rapidly after landing. Very enlarged apical microvilli appeared after 2 days on Earth, suggesting increased choroidal activity. However, as distributions of ezrin and carbonic anhydrase II remained altered in both flight and suspended animals after readaptation to Earth gravity, it was concluded that choroidal structures and functions were not completely restored, even after 2 days in Earth's gravity.

Choroidal readaptation to gravity in rats after spaceflight and head-down tilt

Choroidal responses in microgravity. (SLS-1, SLS-2 and hindlimb-suspension experiments).

Adult male badgers were housed in outdoor pens equipped with an infra‐red actographic system, in the Chize forest (Western France: 46°19'N; 00°24'W). Various parameters characterizing the diurnal general locomotor activity rhythm were measured: duration of the total activity phase and the actual activity outside the burrow in relation to sunset, sunrise or night duration, activity of passage and profile of seasonal variations. Simultaneously the thyroid activity was controlled by bi‐monthly or monthly measurements of plasma thyroxine concentration. 1. In the nycthemeral rhythm of general locomotor activity, there is a close synchronization between the beginning of the activity phase and sunset; nevertheless, from November to March, the beginning of activity occurs 2 h or more after sunset. The end of activity always takes place before the sunrise ("anticipation mechanism") and the delay exhibits a seasonal variation (minimum in summer, maximum in late autumn‐early winter). 2. General locomotor ac...

Daniel Maurel

Papers

Thyroid and gonadal regulation of hair growth during the seasonal molt in the male European badger, Meles meles L

Changes in apical organization of choroidal cells in rats adapted to spaceflight or head-down tilt.

Choroidal readaptation to gravity in rats after spaceflight and head-down tilt

Choroidal responses in microgravity. (SLS-1, SLS-2 and hindlimb-suspension experiments).

Seasonal rhythms of locomotor activity and thyroid function in male badgers (Meles meles L.)