What is the origin of vaginal lubrication?

Vaginal Lubrication: Physiology and Clinical Implications

Vaginal lubrication is primarily an ultrafiltrate created from increased blood flow that is filtered through gap junctions between cells of the vagina. This physiological process is essential for sexual function and comfort during intercourse.

Physiology of Vaginal Lubrication

Vaginal lubrication occurs through a specific physiological mechanism:

• During sexual arousal, increased blood flow to the vaginal tissues is the first measurable sign of arousal 1
• This increased blood flow creates an engorged condition in the vaginal tissues
• The engorgement elevates luminal oxygen tension and stimulates production of surface vaginal fluid
• The fluid is produced through increased plasma transudation (ultrafiltration) that saturates the fluid reabsorptive capacity of the vaginal epithelium 1
• This process appears to be mediated by Vasoactive Intestinal Peptide (VIP), which is present in nerves closely applied to blood vessels in the vaginal wall 1

Key Characteristics of Vaginal Lubrication

• Lubrication increases significantly in response to sexual stimuli and is strongly correlated with self-reported sexual arousal 2, 3
• The process is not blocked by atropine injection, indicating that cholinergic mechanisms are not primarily involved 1
• Lubrication can be objectively measured using tools such as Schirmer Tear Test strips or litmus test strips 2, 3
• Proper lubrication allows for painless penetration and comfortable sexual activity 1

Clinical Relevance and Disorders

Causes of Vaginal Dryness

Several factors can contribute to vaginal dryness:

• Hormonal changes, particularly decreased estrogen levels during menopause 4
• Use of aromatase inhibitors, which is associated with significantly greater incidence of vaginal dryness compared to tamoxifen 4
• Oral contraceptives (can affect vaginal lubrication)
• Smoking (reduces blood flow)
• Douching (disrupts vaginal flora and natural lubrication) 4

Management of Vaginal Dryness

For patients experiencing vaginal dryness, several treatment options exist:

1. Non-hormonal options:

   • Vaginal moisturizers and lubricants for daily comfort and sexual activity 5
   • Water-, oil-, or silicone-based lubricants for sexual activity 5

2. Hormonal options:

   • Low-dose vaginal estrogen (creams, rings, or tablets) for vaginal dryness and dyspareunia 5
   • Vaginal DHEA (prasterone) for vaginal atrophy 4, 5
   • Ospemifene (SERM) for dyspareunia (contraindicated with history of hormone-sensitive cancers) 4, 5

3. Additional approaches:

   • Pelvic floor physical therapy can improve sexual pain, arousal, lubrication, and orgasm 4, 5
   • Topical anesthetics (lidocaine) applied to the vulvar vestibule before penetration for dyspareunia 4

Differential Diagnosis of Female Genital Fluids

It's important to distinguish between different types of fluid expulsion during sexual activity:

• Vaginal lubrication: Ultrafiltrate of blood plasma composed of transvaginal transudate at sexual stimulation 6
• Female ejaculation: Secretion of a few milliliters of thick, milky fluid by the female prostate (Skene's glands) during orgasm 6
• Squirting: Orgasmic transurethral expulsion of larger volumes of fluid (a form of urine containing various concentrations of urea, creatinine, and uric acid) 6
• Coital incontinence: Can be classified into penetration and orgasm forms, associated with stress urinary incontinence or detrusor hyperactivity 6

Clinical Pearls

• Vaginal dryness is a common symptom of sexual dysfunction and can significantly impact quality of life
• Proper assessment should include evaluation of contributing factors such as hormonal status, medications, and sexual arousal concerns
• Treatment should address the underlying cause when possible
• In postmenopausal women, vaginal dryness may worsen with time since menopause, unlike hot flashes which may improve 4
• For patients with a history of hormone-sensitive cancers, non-hormonal options should be considered first 4, 5

Understanding the physiological basis of vaginal lubrication helps guide appropriate clinical assessment and management of related disorders, ultimately improving patients' sexual health and quality of life.